Dokument-ID Dokumenttyp Verfasser/Autoren Herausgeber Haupttitel Abstract Auflage Verlagsort Verlag Erscheinungsjahr Seitenzahl Schriftenreihe Titel Schriftenreihe Bandzahl ISBN Quelle der Hochschulschrift Konferenzname Quelle:Titel Quelle:Jahrgang Quelle:Heftnummer Quelle:Erste Seite Quelle:Letzte Seite URN DOI Abteilungen OPUS4-3107 Wissenschaftlicher Artikel Scheer, Ulrich; Zentgraf, Hanswalter; Sauer, Helmut W. Different chromatin structures in Physarum polycephalum: a special form of transcriptionally active chromatin devoid of nucleosomal particles Nonnucleolar chromatin from interphase nuclei of Physarum polycephalum plasmodia occurs in two different structural configurations as seen in electron microscopic spread preparations. While the majority of the chromatin is devoid of nascent ribonucleoprotein (RNP) fibrils and compacted into nucleosomal particles, a minor proportion (10- 20%) is organized differently and reveals a smooth contour. It is this form of smooth chromatin which is rich in transcription units (mean length: 1.36±0.21 11m). Only occasionally are solitary nascent RNP fibrils observed which are associated with beaded strands of chromatin. In transcribed smooth chromatin nucleosomal particles are not only absent from the transcription units but also from their nontranscribed flan king regions, indicating that this special structural aspect is not merely a direct consequence of the transcriptional process. The existence of ca. 10- 20% of Physarum chromatin in the smoothly contoured form is discussed in relation to reports of a preferential digestibility of a similar proportion of Physarum chromatin by DNAse I (Jalouzot et al. , 1980) and to the altered configuration of "peak A" chromatin subunits after micrococcal nuclease digestion (Johnson et al., 1978a, b). 1981 urn:nbn:de:bvb:20-opus-33148 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3594 Wissenschaftlicher Artikel Thiry, Marc; Scheer, Ulrich; Goessens, Guy Immunoelectron microscopic study of nucleolar DNA during mitosis in Ehrlich tumour cells In order to investigate the DNA localization within Ehrlich tumor cell nucleoli during mitosis, two recent immunocytochemical methods using either an anti-DNA or an anti-bromodeoxyuridine (BrdU) monoclonal antibody have been applied. In both cases, the immunogold labeling has been performed on ultrathin sections of cells embedded either in Lowicryl K4M or in Epon, respectively. Identical results are observed with both immunocytochemical approaches. In the interphase nucleolus, besides the labeling of the perinucleolar chromatin shell and of its intranucleolar invaginations which penetrate into the nucleolar body and often terminate at the fibrillar centers, a few gold particles are also preferentially found towards the peripheral region of the fibrillar centers. In contrast, the dense fibrillar component and the granular component are never labeled. During mitosis, the fibrillar centers persist at the chromosomal nucleolus organizing regions (NOR's) and can be selectively stained by the silver method. However, these metaphase fibrillar centers are no longer decorated by the DNA- or BrdU antibodies. These results indicate that until the end of prophase, rRNA genes are present inside the fibrillar center material, disappear during metaphase and reappear in reconstituting nucleoli during telophase. Thus, fibrillar centers appear to represent structures sui generis, which are populated by rRNA genes only when the nucleolus is functionally active. In segregated nucleoli after actinomycin D treatment, the DNA labeling is exclusively restricted to the perinucleolar chromatin blocks. These findings also suggest that the DNA content of the fibrillar center material varies according to the rRNA transcription level of the cells. The results are discussed in the light of the present knowledge of the functional organization of the nucleolus. 1988 urn:nbn:de:bvb:20-opus-40745 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3595 Wissenschaftlicher Artikel Benavente, Ricardo; Dabauvalle, Marie-Christine; Scheer, Ulrich; Chaly, Nathalie Functional role of newly formed pore complexes in postmitotic nuclear reorganization Many nuclear proteins are released into the cytoplasm at prometaphase and are transported back into the daughter nuclei at the end of mitosis. To determine the role of this reentry in nuclear remodelling during early interphase, we experimentally manipulated nuclear protein uptake in dividing cells. Recently we and others have shown that signal-dependent, pore complex-mediated uptake of nuclear protein is blocked in living cells on microinjection of the lectin wheat germ agglutinin (WGA), or of antibodies such as PI1 that are directed against WGA-binding pore complex glycoproteins. In the present study, we microinjected mitotic PtKz cells with WGA or antibody PIt and followed nuclear reorganization of the daughter cells by immunofluorescence and electron microscopy. The inhibitory effect on nuclear protein uptake was monitored by co-injection of the karyophilic protein nucleoplasmin. When injected by itself early in mitosis, nucleoplasmin became sequestered into the daughter nuclei as they entered telophase. In contrast, nucleoplasmin was excluded from the daughter nuclei in the presence of WGA or antibody PI1 . Although PtKz cells with blocked nuclear protein uptake completed cytokinesis, their nuclei showed a telophaselike organization characterized by highly condensed chromatin surrounded by a nuclear envelope containing a few pore complexes. These findings suggest that pore complexes become functional as early as telophase, in close coincidence with nuclear envelope reformation. They further indicate that the extensive structural rearrangement of the nucleus during the telophase-G1 transition is dependent on the influx of karyophilic proteins from the cytoplasm through the pore complexes, and is not due solely to chromosome- associated components. 1989 urn:nbn:de:bvb:20-opus-40754 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3596 Wissenschaftlicher Artikel Weber, Thomas; Schmidt, Erwin; Scheer, Ulrich Mapping of transcription units on Xenopus laevis lampbrush chromosomes by in situ hybridization with biotin-labeled cDNA probes A non-radioactive in situ hybridization method is described for the localization of transcription units of defined genes to lateral loops of Xenopus laevis lampbrush chromosomes. Two Xenopus cONA probes were used encoding the nucleolar protein N038/ B23 and cytokeratin 1(8). Both proteins are known to be synthesized in Xenopus oocytes, and Northern blot analysis revealed the presence of the corresponding mRNAs in different oogenic stages. The probes were enzymatically labeled with biotin-dCTP and hybridized to lampbrush chromosomes. The sites of hybridization were detected either by indirect immunofluorescence microscopy using rabbit antibodies against biotin and fluorescein-conjugated antirabbit IgG or enzymatically using peroxidase-conjugated streptavi din. The probe encoding the nucleolar protein hybridized to two sets of lateral loops on different bivalents, the cytokeratin probe to at least four. Our finding that each probe hybridized to more than one chromosomal locus may reflect the tetraploid nature of the Xenopus laevis genome or results from cross-hybridization to other transcriptionally active members of the N038/ B23-nucleoplasmin or the cytokeratin-Iamin gene families. The method described should facilitate further in situ hybridization studies with appropriate genomic clones in order to map specific DNA sequences to defined loop regions and to come to a better understanding of the relationship between loop organization and gene transcription unit. 1989 urn:nbn:de:bvb:20-opus-40763 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3597 Wissenschaftlicher Artikel Hügle, Barbara; Scheer, Ulrich; Franke, Werner W. Ribocharin: a nuclear M\(_r\) 40,000 protein specific to precursor particles of the large ribosomal subunit Using a monoclonal antibody (No-194) we have identified, in Xenopus laevis and other amphibia, an acidic protein of M, 40,000 (ribocharin) which is specifically associated with the granular component of the nucleolus and nucleoplasmic 65S particles. These particles contain the nuclear 28S rRNA and apparently represent the precursor to the large ribosomal subunit in nucleocytoplasmic transit. By immunoelectron microscopy ribocharin has been localized in the granular component of the nucleolus and in interchromatin granules. During mitosis ribocharin-containing particles are associated with surfaces of chromosomes and are recollected in the reconstituting nucleoli in late telophase. We suggest that ribocharin is a specific component of precursor particles of the large ribosomal subunit, which dissociates from the 65S particle before passage through the nuclear envelope, and is reutilized in ribosome biogenesis. 1985 urn:nbn:de:bvb:20-opus-41169 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3598 Teil eines Buches Scheer, Ulrich; Zentgraf, Hanswalter Morphology of nucleolar chromatin in electron microscopic spread preparations No abstract available 1982 urn:nbn:de:bvb:20-opus-41155 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3621 Wissenschaftlicher Artikel Franke, Werner W.; Scheer, Ulrich Morphology of transcriptional units at different states of activity The morphology of two forms of transcription ally active chromatin, the nucleoli and the loops of lampbrush chromosomes, has been examined after fixation in situ or after isolation and dispersion of the material in media of low ionic strengths, using a variety of electron microscopic preparation techniques (e.g. spread preparations with positive or negative staining or without any staining at all, with bright and dark field illumination, with autoradiography, after pretreatment of the chromatin with specific detergents such as Sarkosyl NL-30; transmission and scanning transmission electron microscopy of ultrathin sections). Nucleolar chromatin and chromosomes from oocytes of various amphibia and insects as well as from green algae of the family of the Dasycladaceae were studied in particular detail. The morphology of transcriptional units that are densely packed with lateral ribonucleoprotein fibrils, indicative of great transcriptional activity, was compared with that of chromatin of reduced lateral fibril density, including stages of drug-induced inhibition. The micrographs showed that under conditions which preserve the nucleosomal organization in condensed chromatin studied in parallel, nucleosomes are not recognized in transcriptionally active chromatin. This holds for the transcribed regions as well as for apparently untranscribed (i.e. fibril-free) regions interspersed between ('spacer') and/or adjacent to transcribed genes and for the fibril-free regions within transcriptional units of reduced fibril density. In addition, comparison oflengths of repeating units of isolated rDNA with those observed in spread nucleolar chromatin indicated that this DNA is not foreshortened and packed into nucleosomal structures. Granular particles which were observed, at irregular frequencies and in variable patterns, in some spacer regions, did not result in a proportional shortening of the spacer axis, and were found to be resistant to detergent treatment effective in removing most of the chromatin associated proteins including histones. Thus, these particles behave like RNA polymerases rather than nucleosomes. It is suggested that structural changes from nucleosomal packing to an extended form of DNA are involved in the transcriptional activation of chromatin. 1978 urn:nbn:de:bvb:20-opus-41363 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3682 Wissenschaftlicher Artikel Scheer, Ulrich A novel type of chromatin organization in lampbrush chromosomes of Pleurodeles waltlii: visualization of clusters of tandemly repeated, very short transcriptional units A novel chromatin configuration is described in lampbrush chromosomes of Pleurodeles waltlii oocytes which is different from transcriptionally inactive chromatin as weil as from the various forms of transcribed chromatin hitherto described. This novel type of chromatin is not arranged in Christmas tree-Iike configurations of densely packed lateral ribonucleoprotein (RNP) fibriIs but is characterized by a periodic alternating pattern of thick and thin regions which occur in clusters 01 some 10,000 repeats. Each thickened unit with an average length of 45 nm contains two c10sely spaced particles, the putative RNA polymerases, and each thickened unit is separated from the next one by a beaded chromatin spacer with a length of about 80 nm. This chromatin spacer contains on average two particles of approximately 14 nm in diameter, assumed to be nucleosomes. The thickened regions are interpreted to represent short transcriptional units containing approximately 130 base pairs of DNA which are separated from each other by nontranscribed spacers of 240-400 base pairs of DNA. The possibility is discussed that these transcriptional units represent 5S rRNA or tRNA genes. 1982 urn:nbn:de:bvb:20-opus-41087 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3658 Wissenschaftlicher Artikel Benavente, Ricardo; Scheer, Ulrich; Chaly, Nathalie Nucleocytoplasmic sorting of macromolecules following mitosis: fate of nuclear constituents after inhibition of pore complex function PtK2 cells in which pore complex-mediated transport is blocked by microinjection early in mitosis of a monoclonal antibody (specific for an Mr 68000 pore complex glycoprotein) or of wheat germ agglutinin (WGA) complete cytokinesis. However, their nuclei remain stably arrested in a telophase-like organization characterized by highly condensed chromatin and the absence of nucleoli, indicating a requirement for pore-mediated transport for the reassembly of interphase nuclei. We have now examined this requirement more closely by monitoring the behavior of individual nuclear macromolecules in microinjected cells using immunofluorescence microscopy and have investigated the effect of microinjecting the antibody or WGA on cellular ultrastructure. The absence of nuclear transport did not affect the sequestration into daughter nuclei of components such as DNA, DNA topoisomerase I and the nucleolar protein fibrillarin that are carried through mitosis on chromosomes. On the other hand, lamins, snRNAs and the p68 pore complex glycoprotein, all cytoplasmic during mitosis, remained largely cytoplasmic in the telophase-arrested cells. Electron microscopy showed the nuclei to be surrounded by a doublelayered membrane with some inserted pore complexes. In addition, however, a variety of membranous structures with associated pore complexes was regularly noted in the cytoplasm, suggesting that chromatin may not be essential for the postmitotic formation of pore complexes. We propose that cellular compartmentalization at telophase is a two-step process. First, a nuclear envelope tightly encloses the condensed chromosomes, excluding non-selectively all macromolecules not associated with the chromosomes. Interphase nuclear organization is then progressively restored by selective pore complex-mediated uptake of nuclear proteins from the cytoplasm. 1989 urn:nbn:de:bvb:20-opus-40777 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3632 Wissenschaftlicher Artikel Trendelenburg, Michael F.; Franke, Werner W.; Scheer, Ulrich Frequencies of circular units of nucleolar DNA in oocytes of two insects, Acheta domesticus and Dytiscus marginalis, and changes of nucleolar morphology during oogenesis The organization of the extrachromosomal nucleolar material in oocytes of two insect species with different ovary types, the house cricket Acheta domesticus (panoistic ovary) and the water beetle Dytiscus marginalis (meroistic ovary), was studied with light and electron microscopic techniques. Stages early in oogenesis were compared with fully vitellogenic stages (mid-to-Iate diplotene). The arrangement of the nucleolar material undergoes a marked change from a densely aggregated to a dispersed state. The latter was characterized by high transcriptional activity. In spread and positively stained preparations of isolated nucleolar material, a high frequency of small circular units of transcribed rDNA was observed and rings with small numbers (1-5) of pre-rRNA genes were predominant. The observations suggest that the "extra DNA body" observed in early oogenic stages of both species represents a dense aggregate of numerous short circular units of nucleolar chromatin, with morphological subcomponents identifiable in ultrathin sections. These apparently remain in close association with the chromosomal nucleolar organizer(s). The observations further indicate that the individual small nucleolar subunit circles dissociate and are dispersed as actively transcribed rDNA units later in diplotene. The results are discussed in relation to principles of the ultrastructural organization of nucleoli in other cell types as well as in relation to possible mechanisms of gene amplification. 1977 urn:nbn:de:bvb:20-opus-41370 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3633 Wissenschaftlicher Artikel Weber, Klaus; Osborn, Mary; Franke, Werner W.; Seib, Erinita; Scheer, Ulrich; Herth, Werner Identification of microtubular structures in diverse plant and animal cells by immunological cross-reaction revealed in immunofluorescence microscopy using antibodies against tubulin from porcine brain Antibody against tubulin from porcine brain was used to evaluate the immunological cross reactivity of tubulin from a variety of animal and plant cells. Indirect immunofluorescence microscopy revealed microtubule-containing structures including cytoplasmic microtubules, spindle microtubules, cilia and fIagella. Thus tubulin from diverse species of both mammals and plants show immunological cross-reactivity with tubulin from porcine brain. Results obtained by immunofluorescence microscopy are whenever possible compared with previously known ultrastructural results obtained by electron microscopy. 1977 urn:nbn:de:bvb:20-opus-41383 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3634 Wissenschaftlicher Artikel Spring, Herbert; Krohne, Georg; Franke, Werner W.; Scheer, Ulrich; Trendelenburg, Michael F. Homogeneity and heterogeneity of sizes of transcriptional units and spacer regions in nucleolar genes of Acetabularia The arrangement of genes of precursor molecules for ribosomal RNA (pre-rRNA) in primary nuclei from two green algae species, Acetabularia mediterranea and A. major, has been analyzed in an electron microscope study. The pattern of transcriptional units in individual strands of nucleolar chromatin was investigated using spread and positively stained preparations. The rDNA pattern is not uniform but differs in different strands. The predominant type of nucleolar chromatin exhibits a high degree of homogeneity in the sequence of matrix units (intercepts covered with fibrilst hat contain the pre-rRNA) and fibril-free spacer intercepts. Substantial differences, however, are observed between the patterns in different strands. In addition, there is evidence in some strands for intraaxial heterogeneity of both spacer and matrix units. The following major types can be distinguished: type la, ca. 2 micrometer long matrix units, extremely short spacer intercepts in A. mediterranea (ca. 1 micrometer long ones in A. major), completely homogeneous distribution; type Ib, as type la but with intercalated, isolated, significantly shorter and/or longer matrix units; type lIa, matrix unit sizes as in type la, but much longer spacer intercepts, high degree of homogeneity; type Ill, largely heterogeneous arrangements of matrix and spacer units of varying sizes. The matrix unit data are compared with the sizes of pre-rRNA as determined by polyacrylamide gelelectrophoresis under denaturing and non-denaturing conditions. The findings are discussed in relation to recent observations in amphibia and insects and with respect to current concepts of the species-specificity of rDNA arrangements. 1976 urn:nbn:de:bvb:20-opus-41398 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3635 Wissenschaftlicher Artikel Franke, Werner W.; Jarasch, Ernst-Dieter; Herth, Werner; Scheer, Ulrich; Zerban, Heide Cytology : general and molecular cytology The present review discusses some general aspects of membrane structure and problems of membrane isolation and membrane biochemistry, with particular focus on the endoplasmic reticulum. 1975 urn:nbn:de:bvb:20-opus-41458 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3636 Buch (Monographie) Kartenbeck, J.; Zentgraf, H.; Scheer, Ulrich; Franke, Werner W. The nuclear envelope in freeze-etching No abstract available 1971 3-540-05538-X urn:nbn:de:bvb:20-opus-40534 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3637 Wissenschaftlicher Artikel Knecht, Sigrid; Scheer, Ulrich Die Liste der Vogelarten von S. Miguel (Azoren) des Gaspar Fructuoso (gestorben 1591) No abstract available 1972 urn:nbn:de:bvb:20-opus-41402 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3638 Review Reimer, Georg; Raska, Ivan; Tan, Eng M.; Scheer, Ulrich Human autoantibodies: probes for nucleolus structure and function No abstract available 1987 urn:nbn:de:bvb:20-opus-41410 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2702 Wissenschaftlicher Artikel Scheer, Ulrich; Franke, Werner W.; Trendelenburg, Michael F.; Spring, Herbert Classification of loops of lampbrush chromosomes according to the arrangement of transcriptional complexes The arrangement of transcriptional units in the loops of lampbrush chromosomes from oocyte nuclei of urodele amphibia and from primary nuclei of the green alga Acetabularia have been studied in the electron microscope using spread preparations. Loops with different patterns of arrangement of matrix units (i.e. to a first approximation, transcriptional units) can be distinguished: (i) loops consisting of one active transcriptional unit; (ii) loops containing one active transcriptional unit plus additional fibril-free, i.e. apparently untranscribed, intercepts that may include 'spacer' regions; (iii) loops containing two or more transcriptional units arranged in identical or changing polarities, with or without interspersed apparent spacer regions. Morphological details of the transcriptional complexes are described. The observations are not compatible with the concept that one loop reflects one and only one transcriptional unit but, rather, lead to a classification of loop types according to the arrangement of their transcriptional units. We propose that the lampbrush chromosome loop can represent a unit for the coordinate transcription of either one gene or a set of several (different) genes. 1976 urn:nbn:de:bvb:20-opus-32822 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2709 Wissenschaftlicher Artikel Franke, Werner W.; Spring, Herbert; Scheer, Ulrich; Zerban, Heide Growth of the nuclear envelope in the vegetative phase of the green alga Acetabularia. Evidence for assembly from membrane components synthesized in the cytoplasm. No abstract available 1975 urn:nbn:de:bvb:20-opus-32403 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2710 Wissenschaftlicher Artikel Scheer, Ulrich; Franke, Werner W.; Trendelenburg, Michael F. Effects of actinomycin D on the association of newly formed ribonucleoproteins with the cistrons of ribosomal RNA in Triturus oocytes No abstract available 1975 urn:nbn:de:bvb:20-opus-32383 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2711 Wissenschaftlicher Artikel Franke, Werner W.; Kartenbeck, Jürgen; Zentgraf, Hanswalter; Scheer, Ulrich; Falk, Heinz Membrane-to-membrane cross-bridges. A means to orientation and interaction of membrane faces No abstract available 1971 urn:nbn:de:bvb:20-opus-32122 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2712 Wissenschaftlicher Artikel Franke, Werner W.; Scheer, Ulrich; Fritsch, Hansjörg Intranuclear and cytoplasmic annulate lamellae in plant cells No abstract available 1972 urn:nbn:de:bvb:20-opus-32148 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2713 Wissenschaftlicher Artikel Scheer, Ulrich The ultrastructure of the nuclear envelope of amphibian oocytes: a reinvestigation. III. Actinomycin D-induced decrease in central granules within the pores. No abstract available 1970 urn:nbn:de:bvb:20-opus-32110 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2714 Wissenschaftlicher Artikel Wilken, Norbert; Kossner, Ursula; Senécal, Jean-Luc; Scheer, Ulrich; Dabauvalle, Marie-Christine Nup180, a novel nuclear pore complex protein localizing to the cytoplasmic ring and associated fibrils No abstract available 1993 urn:nbn:de:bvb:20-opus-32049 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2715 Wissenschaftlicher Artikel Dabauvalle, Marie-Christine; Loos, Karin; Merkert, Hilde; Scheer, Ulrich Spontaneous assembly of pore complex-containing membranes ("Annulate lamellae") in Xenopus egg extract in the absence of chromatin No abstract available 1991 urn:nbn:de:bvb:20-opus-32797 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2717 Wissenschaftlicher Artikel Scheer, Ulrich; Trendelenburg, Michael F.; Franke, Werner W. Regulation of transcription of genes of ribosomal RNA during amphibian oogenesis: a biochemical and morphological study Natural changes in the transcription of rRNA genes were studied in nucleoli from three oogenic stages of the newt Triturus alpestris with electron microscope, autoradiographic, and biochemical techniques. From determinations of the uridine triphosphate pool sizes and [3H]uridine uptake, phosphorylation, and incorporation into 28S and 18S rRNAs in vivo it was estimated that the rate of rRNA synthesis was about 0.01% in previtellogenic oocytes and 13% in mature oocytes when compared to midvitellogenesis. Spread preparations of nucleoli showed significant morphological changes in the transcriptional complexes. The total number of lateral fibrils, i.e., ribonucleoproteins containing the nascent rRNA precursor, were drastically decreased in stages of reduced synthetic activity. This indicates that rRNA synthesis is regulated primarily at the level of transcription. The resulting patterns of fibril coverage of the nucleolar chromatin axes revealed a marked heterogeneity. On the same nucleolar axis occurred matrix units that were completely devoid of lateral fibrils, matrix units that were almost fully covered with lateral fibrils, and various forms of matrix units with a range of lateral fibril densities intermediate between the two extremes. Granular particles that were tentatively identified as RNA polymerase molecules were not restricted to the transcription l complexes. They were observed, although less regularly and separated by greater distances, in untranscribed spacer regions as well as in untranscribed gene intercepts. The results show that the pattern of transcriptional control of rRNA genes differs widely in different genes, even in the same genetic unit. 1976 urn:nbn:de:bvb:20-opus-32814 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2681 Wissenschaftlicher Artikel Scheer, Ulrich The rifamycin derivative AF/013 is cytolytic No abstract available 1975 urn:nbn:de:bvb:20-opus-32429 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2682 Konferenzveröffentlichung Trendelenburg, Michael F.; Spring, Herbert; Scheer, Ulrich; Franke, Werner W. Morphology of nucleolar cistrons in a plant cell, Acetabularia mediterranea The structural organization of transcriptionally active DNA that contains cistrons for precursor molecules of ribosomal RNA is described in positively stained spread preparations from nuclei and nucleoli isolated from the green alga, Acetabularia mediterranea Lmx. These nuclei contain large aggregates of nucleolar subunits in which fibril-covered regions, the putative active cistrons for precursors of ribosomal RNA, alternate with fibril-free intercepts, the "spacers". The length distribution of the different intercepts of this DNA is given, and the pattern is compared with those shown in animal cell systems. The data are discussed in relation to problems of transcription and of amplification of ribosomal RNA genes. 1974 urn:nbn:de:bvb:20-opus-32213 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2683 Wissenschaftlicher Artikel Scheer, Ulrich; Franke, Werner W. Annulate lamellae in plant cells: formation during microsporogenesis and pollen development in Canna generalis Bailey The occurrence of stacked annulate tamellae is documented for a plant cell system, namely for pollen mother cells and developing pollen grains of Canna generalis. Their structural subarchiteeture and relationship to endoplasmie reticulum (ER) and nuclear envelope cisternae is described in detail. The results demonstrate structural homology between plant and animal annulate lamellae and are compatible with, though do not prove, the view that annulate lamcllar cisternae may originate as a degenerative form of endoplasmic retieulum. 1972 urn:nbn:de:bvb:20-opus-32160 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2684 Wissenschaftlicher Artikel Eckert, W. A.; Franke, Werner W.; Scheer, Ulrich Nucleocytoplasmic translocation of RNA in Tetrahymena pyriformis and its inhibition by actinomycin D and cycloheximide No abstract available 1975 urn:nbn:de:bvb:20-opus-32399 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2685 Wissenschaftlicher Artikel Spring, Herbert; Scheer, Ulrich; Franke, Werner W.; Trendelenburg, Michael F. Lampbrush type chromosomes in the primary nucleus of the green alga Acetabularia mediterranea No abstract available 1975 urn:nbn:de:bvb:20-opus-32370 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2687 Wissenschaftlicher Artikel Zentgraf, Hanswalter; Scheer, Ulrich; Franke, Werner W. Characterization and localization of the RNA synthesized in mature avian erythrocytes No abstract available 1975 urn:nbn:de:bvb:20-opus-32410 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2688 Wissenschaftlicher Artikel Derksen, J.; Trendelenburg, Michael F.; Scheer, Ulrich; Franke, Werner W. Spread chromosomal nucleoli of Chironomus salivary glands No abstract available 1973 urn:nbn:de:bvb:20-opus-32209 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2676 Review Scheer, Ulrich; Thiry, Marc; Goessens, Guy Structure, function and assembly of the nucleolus No abstract available 1993 urn:nbn:de:bvb:20-opus-32057 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2677 Wissenschaftlicher Artikel Franke, Werner W.; Scheer, Ulrich The ultrastructure of the nuclear envelope of amphibian oocytes: a reinvestigation. II. The immature oocyte and dynamic aspects No abstract available 1970 urn:nbn:de:bvb:20-opus-32102 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2678 Wissenschaftlicher Artikel Franke, Werner W.; Trendelenburg, Michael F.; Scheer, Ulrich Natural segregation of nucleolar components in the course of plant cell differentiation Segregation of the nucleolar components is described in the differentiated nucleus of the generative cell in the growing Clivia and Lilium pollen tubes. This finding of a natural nucleolar segregation is discussed against the background of current views of the correlations of nucleolar morphology and transcriptional activity. 1973 urn:nbn:de:bvb:20-opus-32182 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2679 Wissenschaftlicher Artikel Scheer, Ulrich; Trendelenburg, Michael F.; Franke, Werner W. Transcription of ribosomal RNA cistrons: Correlation of morphological and biochemical data Electron microscopic spread preparations of oocyte nucleoli (lampbrush stage) of various amphibians are quantitatively evaluated and the length distributions of repeat-, matrix-, and spacer-units along the rRNA cistron containing axes are given. The correlation of the matrix unit data with the gel electrophoretic pattern of labelled nuclear RNA from the same oocytes is examined. The mean value of the matrix unit corresponds fairly well to a 2.6 million D peak of pre-rRNA but the distribution of both matrix units and labelled pre-rRNAs shows an asymmetrical heterogeneity indicating the existence of some larger primary transcription products of rDNA. Novel structural aspects are described in the spacer regions which suggest that transcription does also take place in DNP regions between the matrix units. A special "prelude piece" coding for approx. 0.5 million D of RNA is frequently visualized in the spacer segments at the beginning of a matrix unit. Possible artifacts resulting from the preparation, the relative congruence between the data obtained using both methods, and the functional meaning of the findings are discussed against the background of current concepts of structural organization and transcription products of nucleolar DNA. 1973 urn:nbn:de:bvb:20-opus-32195 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2680 Wissenschaftlicher Artikel Dabauvalle, Marie-Christine; Loos, Karin; Scheer, Ulrich Identification of a soluble precursor complex essential for nuclear pore assembly in vitro No abstract available 1990 urn:nbn:de:bvb:20-opus-32801 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3329 Wissenschaftlicher Artikel Scheer, Ulrich; Schmidt-Zachmann, Marion S.; Hügle, Barbara; Franke, Werner W. Identification and localization of a novel nucleolar protein of a high molecular weight by a monoclonal antibody A monoclonal murine antibody (No-I 14) is described which reacts specifically with a polypeptide of molecular weight (M,) 180000 present in low-speed nuclear pellets from oocytes and somatic cells of Xenopus laevis and X. borealis and in isolated amplified nucleoli. Two-dimensional gel electrophoresis has revealed the acidic nature of this polypeptide (isoelectric at pH of ca 4.2 in the presence of 9.5 M urea). A relatively large proportion of the protein is extracted at elevated ionic strength( i.e., at 0.4-0.5 M alkali salt) in a form sedimenting at approx. 7-8S , compatible with a monomeric state. It is also extracted by digestion with RNase but not with DNase. In immunofluorescence microscopy, antibody No-114 stains intensely nucleoli of oocytes and all somatic cells examined , including the residual nucleolar structure of Xenopus erythrocytes which are transcriptionally inactive. During mitosis the antigen does not remain associated with the nucleolar organizer regions (NOR) of chromosomes but is released and dispersed over the cytoplasm until telophase when it re-associates with the reforming interphase nucleoli. At higher resolution the immunofluorescent region is often resolved into a number of distinct subnucleolar components of varied size and shape. Immunoelectron microscopy using colloidal gold-coupled secondary antibodies reveals that the M, 180000 protein is confined to the dense fibrillar component of the nucleolus. This conclusion is also supported by its localization in the fibrillar part of segregated nucleoli of cells treated with actinomycin D. We conclude that nucleoli contain a prominent protein of M, 180000 which contributes to the general structure of the dense fibrillar component of the interphase nucleolus , independent of its specific transcriptional activity. 1984 urn:nbn:de:bvb:20-opus-39786 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3330 Wissenschaftlicher Artikel Scheer, Ulrich; Sommerville, J. Structural organization of nascent transcripts and hnRNA molecules in amphibian oocytes Comparisons ofrelative lengths oflampbrush loops, nascent RNP transcripts and hnRNA molecules from oocytes of amphibia with different C-values show that there is an increasing trend in loop, and transcriptional unit, length with increase in genome size but no increasing trend with respect to RN A contour length.The formation of duplex regions and circles in RNP fibrils indicates that RNA processing may occur within the nascent fibrils. The hnRNA molecules from oocytes of the various amphibia readily form intermolecular duplex structures. These complementary sequences have a low kinetic complexity and are transcribed from highly repetitive sequences distributed throughout the genome. Their possible function is considered. 1981 urn:nbn:de:bvb:20-opus-39765 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3331 Teil eines Buches Scheer, Ulrich; Franke, Werner W. Structures and functions of the nuclear envelope No abstract available 1974 urn:nbn:de:bvb:20-opus-39777 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3332 Wissenschaftlicher Artikel Scheer, Ulrich Changes of nucleosome frequency in nucleolar and non-nucleolar chromatin as a function of transcription: an electron microscopic study The morphology of nucleolar and non-nucleolar (Iampbrush chromosome loops) chromatin was studied in the electron microscope during states of reduced transcriptional activity in amphibian oocytes (Xenopus laevis, Triturus alpestris, T. cristatus). Reduced transcriptional activity was observed in maturing stages of oocyte development and after treatment with an inhibitor, actinomycin D. Strands of nucleolar chromatin appear smooth and thin, and contain only few, if any, nucleosomal particles in the transcribed units. This is true whether they are densely or only sparsely covered with lateral ribonucleoprotein fibrils. This smooth and non-nucleosomal character is also predominant in the interspersed, apparently nontranscribed rDNA spacer regions. During inactivation, however, nucleolar chromatin frequently and progressively assumes a beaded appearance in extended fibril-free-that is, apparently nontranscribed - regions. I n either fUll-grown 00- cytes or late after drug treatment, most of the nucleolar chromatin is no longer smooth and thin, but rather shows a beaded configuration indistinguishable from inactive non - nucleolar chromatin. In many chromatin strands, transitions of fibril-associated regions of smooth character into beaded regions wihout lateral fibrils are seen. Similarly, in the non-nucleolar chromatin of the retracting lampbrush chromosome loops, reduced transcriptional activity is correlated with a change from smooth to beaded morphology. Here, however, beaded regions are also commonly found interspersed between the more or less distant bases of the lateral fibrils, the putative transcriptional complexes. I n both sorts of chromatin, detergents (in particular Sarkosyl) that remove most of the chromatin proteins including histones from the DNA axis but leave the RNA polymerases of the transcriptional complexes attached were used to discriminate between polymerases and nucleosomal particles. The results suggest that nucleosomes are absent in heavily transcribed chromatin regions but are reformed after inactivation. In contrast to the findings with inactivated nucleolar genes, in lampbrush chromosome loops the beaded nucleosomal configuration appears to be assumed also in regions within transcriptional units that, perhaps temporarily, are not involved in transcription. 1978 urn:nbn:de:bvb:20-opus-39750 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3333 Wissenschaftlicher Artikel Scheer, Ulrich; Hansmann, Paul; Falk, Heinz; Sitte, Peter Ultrastructural localization of DNA in two Cryptomonas species by use of a monoclonal DNA-antibody Immunogold cytochemistry - DNA localization - Cryptomonas nucleomorph The distribution and subcellular localization of DNA in the unicellular alga Cryptomonas has been investigated electron-microscopically by indirect immunocytochemistry, using a monoclonal DNA antibody and a gold-Iabeled secondary antibody. This technique proved to be very sensitive and entirely specific. DNA could be demonstrated in four different compartments (nucleus, nucleomorph, plastid, and mitochondrion). Within the plastid, DNA is concentrated in stroma regions that are localized preferentially around the center of the organelle. The mitochondrion contains several isolated DNA-containing regions (nucleoids). Within the nucleus, most of the DNA is localized in the 'condensed' chromatin. DNA was also detectable in small areas of the nucleolus, whereas the interchromatin space of the nucleus appeared almost devoid of DNA. Within the nucleomorph, DNA is distributed inhomogeneously in the matrix. DNA could furthermore be detected in restricted areas of the 'fibrillogranular body' of the nucleomorph, resembling the situation encountered in the nucleol us. The presence of DNA and its characteristic distribution in the nucleomorph provide additional, strong evidence in favour of the interpretation of that organelle as the residual nucleus of a eukaryotic endosymbiont in Cryptomonas. 1986 urn:nbn:de:bvb:20-opus-39746 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3203 Wissenschaftlicher Artikel Rose, Kathleen M.; Szopa, Jan; Han, Fu-Sheng; Cheng, Yung-Chi; Richter, Arndt; Scheer, Ulrich Association of DNA topoisomerase I and RNA polymerase I: A possible role for topoisomerase I in ribosomal gene transcription RNA polymerase I preparations purified from a rat hepatoma contained DNA topoisomerase activity. The DNA topoisomerase associated with the polymerase had an Mr of 110000, required Mg2+ but not ATP, and was recognized by anti-topoisomerase I antibodies. When added to RNA polymerase I preparations containing topoisomerase activity, anti-topoisomerase I antibodies were able to inhibit the DNA relaxing activity of the preparation as well as RNA synthesis in vitro. RNA polymerase II prepared by analogous procedures did not contain topoisomerase activity and was not recognized by the antibodies. The topoisomerase I: polymerase I complex was reversibly dissociated by column chromatography on Sephacryl S200 in the presence of 0.25 M (NH4hS04. Topoisomerase I was immunolocalized in the transcriptionally active ribosomal gene complex containing RNA polymerase I in situ. These data indicate that topoisomerase I and RNA polymerase I are tightly complexed both in vivo and in vitro, and suggest a role for DNA topoisomerase I in the transcription of ribosomal genes. 1988 urn:nbn:de:bvb:20-opus-33901 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3204 Wissenschaftlicher Artikel Scheer, Ulrich; Franke, Werner W. Negative staining and adenosine triphosphatase activity of annulate lamellae of newt oocytes Semi -iso la ted annul a te lamellae were prepared from single newt oocy tes (Triturus alpestris) by a modified Call a n-T omlin technique. Such preparations were examined with the electron mi croscope, and the negative sta ining a ppearance of th e a nnulate lamellae is described . The annul a te lamellae can be de tected either adhering to the nuclear envelope or being detached from it. Sometimes they a re obse rved to be connected with slender tubular-like structures interpreted as pa rts of the endoplasmic reti culum. The results obta ined from negativ e sta ining a re combined with those from sections. Especially, the structural data on th e a nnula te lamellae and the nuclear envelope of the very same cell were compa red . Evidence is presented th a t in the oocytes studied the two kinds of porous cisternae, n amely a nnul a te lamellae and nuclear envelope, a re markedly distinguished in that the annul a te lamellae ex hibit a much higher pore frequency (generally about twice tha t found for the corresponding nuclear envelope) and have al so a rela tive pore area occupying as much as 32 % to 55 % of th e cistern al surface (compa red with 13 % to 22 % in the nuclear envelopes). T he pore di ame ter a nd all other ultras tructural details of the pore complexes, however, a re equi valent in both kinds of porous cisternae. Like the annuli of the nuclear pore complexes of various a nimal and pl ant cells, the a nnuli of the a nnula te lamellae pores reveal al so an eightfold symmetry of their subunits in negatively stained as well as in ectioned ma teria l. Furthermore, th e a nnul a te lamellae a re shown to be a site of activity of the Mg-Na-Kstimul a ted ATPase. 1969 urn:nbn:de:bvb:20-opus-32087 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3205 Wissenschaftlicher Artikel Scheer, Ulrich Nuclear pore flow rate of ribosomal RNA and chain growth rate of its precursor during oogenesis of Xenopus laevis The number of ribosomal RNA molecules which are transferred through an average nuclear pore complex per minute into the cytoplasm (nuclear pore flow rate, NPFR) during oocyte growth of Xenopus laevis is estimated. The NPFR calculations are based on determinations of the increase of cytoplasmic rRNA content during defined time intervals and of the total number of pore complexes in the respective oogenesis stages. In the mid-la mpbrush stage (500:"700 I'm oocyte diameter) the NPFR is maximal with 2.62 rRNA molecules/ pore/ minute. Then it decreases to zero at the end of oogenesis. The nucleocytoplasmic RNA f10w rates determined are compared with corresponding values of other cell types. The molecular weight of the rRNA precursor transcribed in the extrachromosomal nucleoli of Xenopus lampbrush stage oocytes is determined by acrylamide gel electrophoresis to be 2.5 x 10· daltons. From the temporal increase of cytoplasmic rRNA (3.8 I'g per oocyte in 38 days) and the known number of simultaneously growing precursor molecules in the nucleus the chain growth rate of the 40 S precursor RNA is estimated to be 34 nucleotides per second. 1973 urn:nbn:de:bvb:20-opus-32178 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3206 Wissenschaftlicher Artikel Franke, Werner W.; Berger, S.; Falk, Heinz; Spring, H.; Scheer, Ulrich; Trendelenburg, Michael F.; Schweiger, H. G.; Herth, W. Morphology of the nucleo-cytoplasmic interactions during the development of Acetabularia cells. I. The vegetative phase The ultrastructure of th e growin g and ma turing primary nucleus of Acetabularia medite rranea and Acetabularia major has been studied with the use of various fi xation procedures. Particular interest has been focused on the deta ils of the nuclear periphery and the perinuclear region. It is demonstrated that early in nuclear grow th a characteristic perinucl ear structura l complex is formed which is, among the eukaryotic cells, unique to Acetabularia and re lated genera. This perinuclear system consists essentially of a) the nuclear envelope with a very hi gh pore frequency and various pore complex assoc iat ion s w ith granular and/or threadlike structures some of which are continuous with the nucleolus; b) an approx imate ly 100 nm thick intermediate zone densely filled with a filam entOus material and occasional sma ll membraneous structures from which the typical cytOplasmic and nuclear organe lles and particles are excl ud ed ; c) an adjacent Iacunar labyrinthum which is interrupted by many plasmatic junction channels between the intermed iate zone and the free cytOplasm; d) numerous dense perinuclear bodies in the juxtanuclear cytOplasm which a re especia lly frequent at the junction channels and reveal a composition of aggregated fibrillar and granul ar structures; e) very dense exclusively fibrill ar agg regates which occur either in assoc iation with t he perinuclear region of the lacunar labyrinthum or, somewhat further out, in the cytOplasmic strands between the bra nches of the lacun ar labyrinthum in the form of slender, characteristic rods or "sausages". 1974 urn:nbn:de:bvb:20-opus-32363 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3207 Wissenschaftlicher Artikel Benavente, Ricardo; Rose, Kathleen M.; Reimer, Georg; Hügle-Dörr, Barbara; Scheer, Ulrich Inhibition of nucleolar reformation after microinjection of antibodies to RNA polymerase I into mitotic cells The formation of daughter nuclei and the reformation of nucleolar structures was studied after microinjection of antibodies to RNA polymerase I into dividing cultured cells (PtK2). The fate of several nucleolar proteins representing the three main structural subcomponents of the nucleolus was examined by immunofluorescence and electron microscopy. The results show that the RNA polymerase I antibodies do not interfere with normal mitotic progression or the early steps of nucleologenesis, i.e. , the aggregation of nucleolar material into prenucleolar bodies. However,they inhibit the telophasic coalescence of the prenucleolar bodies into the chromosomal nucleolar organizer regions, thus preventing the formation of new nucleoli. These prenucleolar bodies show a fibrillar organization that also compositionally resembles the dense fibrillar component of interphase nucleoli . We conclude that during normal nucleologenesis the dense fibrillar component forms from preformed entities around nucleolar organizer regions, and that this association seems to be dependent on the presence of an active form of RNA polymerase I. 1987 urn:nbn:de:bvb:20-opus-33247 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3208 Wissenschaftlicher Artikel Sommerville, John; Scheer, Ulrich Transcription of complementary repeat sequences in amphibian oocytes Repeat sequences are transcribed in the germinal vesicles of amphibian oocytes. In the hnRNA population both complements of the repeats are found and can be readily detected because they form intermolecular duplex structures. The structure and formation of duplex regions have been studied in the hnRNA of Xenopus laevis, Triturus cristatus, Amphiuma means and Necturus maculosus, a series of amphibians of increasing genome size (C-value). In T. cristatus, the duplex structures are mostly 600- 1200 bp in length, whereas in X. laevis they are shorter and in N. maculosus they tend to be longer. Although the proportion of RNA sequence capable of rapidly forming duplex structures is different in different organisms, this property bears no relationship to C-value. However the sequence complexity of complementary repeats, as estimated from the rate of duplex formation, does show an increasing trend with C-value. The complementary repeats found in oocyte hnRNA are transcribed from families of DNA sequence that are each represented in the genome by thousands of copies. The extent of cross-species hybridization is low, indicating that the repeat sequences transcribed in different amphibian genera are not the same. In situ hybridization experiments indicate that the repeat sequences are spread throughout the genome. The evolution and possible function of complementary repeats are considered. 1982 urn:nbn:de:bvb:20-opus-33915 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3209 Wissenschaftlicher Artikel Reimer, Georg; Raska, Ivan; Scheer, Ulrich; Tan, Eng M. Immunolocalization of 7-2-ribonucleoprotein in the granular component of the nucleolus Certain autoimmune sera contain antibodies against a nucleolar ribonucleoprotein particle associated with 7-2-RNA (R. Reddy et al. (1983) J. Bioi. Chem . 258, 1383; C. Hashimoto and J. A. Steitz (1983) J. Bioi. Chem. 258, 1379). In this study, we showed by immunofluorescence microscopy that antibodies reactive with 7-2-ribonucleoprotein immunolocalized in the granular regions of actinomycin D and 5,6-dichloro-I-j3-D-ribofuranosylbenzimidazole (DRB)-segregated nucleoli from Vero cells. By electron microscopic immunocytochemistry, antigen-antibody complexes were located in the granular component of transcriptionally active nucleoli from rat liver hepatocytes and HeLa cells. Anti-7- 2-RNP antibodies from two autoimmune sera immunoprecipitated a major protein of Mr 40,000 from e5S] methionine-Iabeled HeLa cell extract. The immunolocalization data suggest that 7-2-ribonucleoprotein may be involved in stages of ribosome biogenesis which take place in the granular component of the nucleolus, i.e., assembly, maturation, and/or transport of preribosomes 1988 urn:nbn:de:bvb:20-opus-33890 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3356 Teil eines Buches Scheer, Ulrich Contributions of electron microscopic spreading preparations ("Miller-spreads") to the analysis of chromosome structure No abstract available 1987 urn:nbn:de:bvb:20-opus-39625 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3357 Wissenschaftlicher Artikel Scheer, Ulrich; Raska, I. Immunocytochemical localization of RNA polymerase I in the fibrillar centers of nucleoli No abstract available 1987 urn:nbn:de:bvb:20-opus-39618 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3362 Wissenschaftlicher Artikel Trendelenburg, Michael F.; Scheer, Ulrich; Franke, W. W. Structural organization of the transcription of ribosomal DNA in oocytes of the house cricket No abstract available 1973 urn:nbn:de:bvb:20-opus-33113 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3363 Wissenschaftlicher Artikel Scheer, Ulrich; Kartenbeck, Jürgen; Trendelenburg, Michael F.; Stadler, Joachim; Franke, Werner W. Experimental disintegration of the nuclear envelope: evidence for pore-connecting fibrils The disintegration of the nuclear envelope has been examined in nuclei and nuclear envelopes isolated from amphibian oocytes and rat liver tissue, using different electron microscope techniques (ultrathin sections and negatively or positively stained spread preparations). Various treatments were studied, including disruption by surface tension forces, very low salt concentrations, and non ionic detergents such as Triton X-lOO and Nonidet P-40. The high local stability of the cylinders of nonmembranous pore complex material is emphasized. As progressive disintegration occurred in the membrane regions, a network of fibrils became apparent which interconnects the pore complexes and is distinguished from the pore complexassociated intranuclear fibrils. This network might correspond to an indistinct lamella, about 15 - 20 nm thick, located at the level of the inner nuclear membrane, which is recognized in thin sections to bridge the interpore distances. With all disintegration treatments a somewhat higher susceptibility of the outer nuclear membrane is notable, but a selective removal does not take place. Final stages of disintegration are generally characterized by the absence of identifiable, membrane- like structures. Analysis of detergent-treated nuclei and nuclear membrane fractions shows almost complete absence of lipid components but retention of significant amount of glycoproteins with a typical endomembrane-type carbohydrate pattern. Various alternative interpretations of these observations are discussed. From the present observations and those of Aaronson and Blobel (1,2), we favor the notion that threadlike intrinsic membrane components are stabilized by their attachment to the pore complexes, and perhaps also to peripheral nuclear structures, and constitute a detergent-resistant, interpore skeleton meshwork. 1976 urn:nbn:de:bvb:20-opus-39735 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3349 Wissenschaftlicher Artikel Franke, Werner W.; Scheer, Ulrich; Spring, Herbert; Trendelenburg, Michael F.; Krohne, G. Morphology of transcriptional units of rDNA: evidence for transcription in apparent spacer intercepts and cleavages in the elongating nascent RNA Several types of "irregular" structures in the arrangement of lateral fibrils were noted in electron microscopic preparations of transcriptionally active nucleolar chromatin from various plant and animal cells. Such forms include: I. Disproportionately long lateral fibrils which occur either as individual fibrils or in groups; 2. "Prelude complexes" and other arrangements of lateral fibrils in apparent spacer intercepts; 3. Thickening of the rDNA chromatin axis at the starting end of pre-rRNA matrix units; 4. Extremely long matrix units , the length of which exceeds that of the rDNA (double-strand) sequence complementary to the specific pre-rRN A (for abbreviations see text). In addition, the stability of high molecular weight RNAs contained in the nucleolar ribonucleoproteins during the preparation for electron microscopy was demonstrated by gel electrophoresis. The observations indicate that the morphological starting point of a pre-rRNA matrix unit is not necessarily identical with the initiation site for synthesis of pre-rRNA, but they rather suggest that the start of the transcriptional unit is located at least O.2-D.8 JLm before the matrix unit and that parts of the "apparent spacer" are transcribed. It is proposed that the pre-rRN A molecules do not represent the primary product of rDNA transcription but rather relatively stable intermediate products that have already been processed during transcription. 1976 urn:nbn:de:bvb:20-opus-39681 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3350 Wissenschaftlicher Artikel Scheer, Ulrich; Knecht, Sigrid Die Vögel der Azoren Während einer viermonatigen Reise zu allen neun Azoreninseln wurde der gesamte Brutvogelbestand dieses Archipels untersucht. Die Befunde sind in einer detaillierten Artenliste zusammengefaßt, ergänzt durch ökologische und brutbiologische Anmerkungen. Zahlreiche Beobachtungen lassen vermuten, daß vor allem Stieglitz und Kanarienvogel tägliche und auch jahreszeitlich bedingte interinsulare Flüge unternehmen. Die Lautäußerungen sechs verschiedener Vogel arten sind in Klangspektrogrammen dargestellt. Ein mathematischer Ansatz zeigt, daß sich die Anzahl der auf einer bestimmten Insel brütenden Landvogelarten umgekehrt proportional zur Entfernung zum europäischen Festland und proportional zum Logarithmus naturalis der Inselfläche verhält. Die abgeleitete Formel läßt sich prinzipiell auch auf andere Atlantikinseln anwenden, die weitgehend vom Festland isoliert sind. 1971 urn:nbn:de:bvb:20-opus-39668 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3351 Wissenschaftlicher Artikel Scheer, Ulrich Biologische Objekte im Transmissions-Elektronenmikroskop (Teil 4): Spreitungstechniken Visualizing nucleic acids (DNA, RNA), nucleoprotein complexes and chromatin requires the use of special electron microscopicspreading techniques. In part 4 (27 refs.), methods are outlined for spreading DNA and RNA molecules for electron microscopic observation, these methods using modifications of the basic protein film method developed by A. Kleinschmidt and R. K. Zahn (1959). Hybridization techniques that allow the observation of heteroduplexes formed between two DNA molecules or between DNA and RNA molecules are reviewed, with special emphasis being placed on the DNA-RNA hybrids as a tool for elucidating RNA splicing. Techniques for studying DNA-protein interactions without the use of a protein monolayer film are mentioned. Finally, the "Miller spreading technique" for visualizing the nucleosomal organization of eukaryotic chromatin as well as the transcription of genes is discribed and illustrated. 1982 urn:nbn:de:bvb:20-opus-39652 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3352 Wissenschaftlicher Artikel Franke, Werner W.; Scheer, Ulrich Structural details of dictyosomal pores Structural details of the dictyosomal pores in several plant cell types are described from tangential and cross sections of Golgi cisternae. Frequency distributions of the sizes of such Golgi pores are given and compared with the corresponding values of nuclear pores in the same cells. Golgi pore inner diameters are less homogeneously distributed and can be as small as 100 A or less. They are not simply cisterna I holes, but are often associated with centrally located electron dense granules or rods and with inner pore filaments. This organization, which is very common in dictyosomal pores in plant and animal cells, has some similarities with the structural architecture of nuclear envelope and annulate lamellar pore complexes. The particulate material associated with the dictyosomal pores shows spatial and structural relationship to cytoplasmic ribosomes. Possible modes of Golgi pore formation and some consequences of these observations for interpretation of nuclear pore structures are discussed. 1972 urn:nbn:de:bvb:20-opus-32155 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3353 Wissenschaftlicher Artikel Fischer, Dagmar; Hock, Robert; Scheer, Ulrich DNA Topoisomerase II is not detectable on lampbrush chromosomes but enriched in the amplified nucleoli of xenopus oocytes In somatic cells DNA topoisomerase II (topo II) is thought to be involved in the domain Organization of the genome by anchoring the basis of chromatin loops to a chromosomal scafFold. Lampbrush chromosomes of am-phibian oocytes directly display this radial loop Organization in cytological preparations. In order to find out whether topo II may play a role in the Organization of these meiotic chromosomes, we performed immunofluorescence studies using antibodies against Xenopus topo II. Our results indicate that topo II is apparently absent from lampbrush chromosomes and is hence unlikely to act as a "fastener" of the numerous lateral chromosomal loops. Topo II was, however, enriched in the amplified nucleoli of Xenopus oocytes. 1993 urn:nbn:de:bvb:20-opus-32654 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3374 Wissenschaftlicher Artikel Benavente, Ricardo; Schmidt-Zachmann, Marion S.; Hügle-Dörr, B.; Reimer, G.; Rose, K. M.; Scheer, Ulrich Identification and definition of nucleolus-related fibrillar bodies in micronucleated cells Small nucleolus-related bodies which occur in the nUcleoplasm of " micronuclei" lacking nucleolar organizers have been studied by immunofluorescence microscopy. These bodies stained specifically with three different antibodies directed against proteins that are normally associated with the dense fibrillar component of functional nucleoli, but not with antibodies specific for certain proteins of the granular component or the fibrillar centers. Our data show that, in the absence of rRNA genes, the various constituent proteins characteristic of the dense fibrillar component spontaneously assemble into spherical entities but that the subsequent fusion of these bodies into larger structures is prevented in these micronuclei. The similarity between these nucleolus-related bodies of micronuclei and the prenucleolar bodies characteristic of early stages of nucleologenesis during mitotic telophase is discussed. 1988 urn:nbn:de:bvb:20-opus-39423 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3375 Teil eines Buches Franke, Werner W.; Scheer, Ulrich; Spring, Herbert; Trendelenburg, Michael F.; Zentgraf, Hanswalter Organization of nucleolar chromatin No abstract available 1979 urn:nbn:de:bvb:20-opus-39410 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3380 Teil eines Buches Scheer, Ulrich; Spring, Herbert; Trendelenburg, Michael F. Organization of transcriptionally active chromatin in lampbrush chromosome loops No abstract available 1979 urn:nbn:de:bvb:20-opus-39293 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3381 Wissenschaftlicher Artikel Thiry, Marc; Scheer, Ulrich; Goessens, Guy Localization of DNA within Ehrlich tumour cells nucleoli by immunoelectron microscopy The distribution of DNA in Ehrlich tumour cell nucleoli was investigated by means of an immunocytochemical approach , involving a monoclonal antibody directed against double- and single-stranded DNA. Immunolabelling was performed . either before or after the embedding process. The postembedding labelling method allows better ultrastructural preservation than the preembedding labelling method. In particular, the various nucleolar components are well preserved and identifiable. In the nucleolus, labelling is particularly concentrated over the perinucleolar chromatin and over its intranucleolar invaginations, which penetrate the nucleolar body and often terminate at the fibrillar centres. In addition, aggregates of gold particles are found in the fibrillar centres, preferentially towards the peripheral regions. By contrast, the dense fibrillar component is completely devoid of labelling. The results seem to indicate that DNA containing the rDNA genes is located in the fibrillar centres, with a preference for the peripheral regions. This finding suggests that transcription of the rDNA genes should occur within the confines of the fibrillar centre, probably close to the boundary region of the surrounding dense fibrillar component. The results are discussed in the light of present knowledge of the functional organization of the nucleolus. 1988 urn:nbn:de:bvb:20-opus-39327 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3382 Wissenschaftlicher Artikel Scheer, Ulrich Structure of lampbrush chromosome loops during different states of transcriptional activity as visualized in the presence of physiological salt concentrations Lampbrush chromosomes of amphibian oocytes were isolated in the presence of near-physiological salt concentrations, to preserve their native state, and studied by electron microscopy of ultrathin s~dions. The transcriptional state of the lampbrush chromosomes was experimentally modulated by incubating the oocytes for various time periods in medium containing actinomycin D. The observations show that the structure of the lateral loops changes rapidly in response to alterations in transcriptional activity. During decreasing transcriptional activity and reduced packing density of transcripts, the chromatin axis first condensed into nucleosomes and then into an approximately 30 nm thick higher order chromatin fiber. Packaging of the loop axis into supranucleosomal structures may contribute to the foreshortening and retraction of the loops observed during inhibition of transcription and in later stages of meiotic prophase. The increasing packing density of the DNA during the retraction process of the loops could also be visualized by immunofluorescence microscopy using antibodies to DNA. The dependence of the loop chromatin structure on transcriptional activity is discussed in relation to current views of mechanisms involved in gene activation. 1987 urn:nbn:de:bvb:20-opus-39304 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3421 Review Fischer, Dagmar; Weißenberger, Dieter; Scheer, Ulrich Assigning functions to nucleolar structures Nucleoli provide the fascinating possibility of linking morphologically distinct structures such as those seen in the electron microscope with biochemical f eatures of the formation and step wise maturation of ribosomes. Localization of proteins by immunocytochemistry and of rRNA genes and their transcripts by in situ hybridization has greatly improved our understanding of the structural-functional relationships of the nucleolus. The present review describes some recent results obtained by electron microscopic in situ hybridization and argues that this approach has the potential to correlate each step of the complex pre-rRNA maturation pathway with nucleolar structures. Evidence is accumulating that the nucleolus-specific U3 snRNPs (small nuclear ribonucleoprotein particles) participate in rRNA processing events, similar to the role played by the nucleoplasmic snRNPs in mRNA maturation. The intranucleolar distribution of U3 snRNA is consistent with the view that it is involved in both early and late stages of pre-rRNA processing. 1991 urn:nbn:de:bvb:20-opus-34258 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3335 Wissenschaftlicher Artikel Scheer, Ulrich; Hinssen, Horst; Franke, Werner W.; Jockusch, Brigitte M. Microinjection of actin-binding proteins and actin antibodies demonstrates involvement of nuclear actin in transcription of lampbrush chromosomes Nuclei of amphibian oocytes contain large amounts of actin, mostly in unpolymerized or short-polymer form. When antibodies to actin or actin-binding proteins (fragmin and the actin modulator from mammalian smooth muscle) are injected into nuclei of living oocytes of Pleurodeles waltlii, transcription of the lampbrush chromosomes, but not of the rRNA genes, is inhibited. When transcription is repressed by drugs or RNA is digested by microinjection of RNAase into oocyte nuclei, an extensive meshwork of actin filament bundles is seen in association with the isolated lampbrush chromosomes. These observations indicate a close relationship between the state of nuclear actin and transcriptional activity and suggest that nuclear actin may be involved in transcriptional events concerning protein-coding genes. 1984 urn:nbn:de:bvb:20-opus-39706 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3336 Wissenschaftlicher Artikel Hügle, Barbara; Hazan, Rachel; Scheer, Ulrich; Franke, Werner W. Localization of ribosomal protein S1 in the granular component of the interphase nucleolus and its distribution during mitosis Using antibodies to various nucleolar and ribosomal proteins, we define, by immunolocalization in situ, the distribution of nucleolar proteins in the different morphological nucleolar subcompartments. In the present study we describe the nucleolar localization of a specific ribosomal protein (51) by immunofluorescence and immunoelectron microscopy using a monoclonal antibody (R5 1-105). In immunoblotting experiments, this antibody reacts specifically with the largest and most acidic protein of the small ribosomal subunit (51) and shows wide interspecies cross-reactivity from amphibia to man. Beside its localization in cytoplasmic ribosomes, this protein is found to be specifically localized in the granular component of the nucleolus and in distinct granular aggregates scattered over the nucleoplasm. This indicates that ribosomal protein 51, in contrast to reports on other ribosomal proteins, is not bound to nascent pre-rRNA transcripts but attaches to preribosomes at later stages of rRNA processing and maturation. This protein is not detected in the residual nucleolar structures of cells inactive in rRNA synthesis such as amphibian and avian erythrocytes. During mitosis, the nucleolar material containing ribosomal protein 51 undergoes a remarkable transition and shows a distribution distinct from that of several other nucleolar proteins. In prophase, the nucleolus disintegrates and protein 51 appears in numerous small granules scattered throughout the prophase nucleus. During metaphase and anaphase, a considerable amount of this protein is found in association with the surfaces of all chromosomes and finely dispersed in the cell plasm. In telophase, protein 51-containing material reaccumulates in granular particles in the nucleoplasm of the newly formed nuclei and, finally, in the re-forming nucleoli. These observations indicate that the nucleolus-derived particles containing ribosomal protein 51 are different from cytoplasmic ribosomes and, in the living cell, are selectively recollected after mitosis into the newly formed nuclei and translocated into a specific nucleolar subcompartment, i.e ., the granular component. The nucleolar location of ribosomal protein 51 and its rearrangement du'ring mitosis is discussed in relation to the distribution of other nucleolar proteins. 1985 urn:nbn:de:bvb:20-opus-39695 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3337 Wissenschaftlicher Artikel Scheer, Ulrich; Sommerville, John; Müller, Ulrike DNA is assembled into globular supranucleosomal chromatin structures by nuclear contents of amphibian oocytes The assembly of DNA into nucleosomal and supranucleosomal chromatin structures has been studied (i) by injection of circular DNA molecules (plasmids) into nuclei of Pleurodeles waltlii oocytes; and (ii) by in vitro incubation of plasmid molecules with the supernatant fraction from oocyte nuclei of Pleurodeles and Xenopus laevis, followed by purification of nucleoprotein structures formed with sucrose gradient centrifugation. [n both types of experiments , spread preparations of the newly assembled and transcriptionally inactive chromatin , examined by electron microscopy , show dense globular higher order (supranucleosomal) packing forms. Under partially relaxing (low salt) preparation conditions granular chromatin subunits of about 30 nm diameter can be seen either as widely spaced particles or in closely packed aggregates. The transcriptionally inactive endogenous chromatin of chromomeres of lampbrush chromosomes is arranged in similar higher order chromatin units. A correlation is found between the sizes of the DN A molecule probes used and the numbers of nucleosomes and higher order globules in the assembled chromatin structures. After prolonged dispersion in low salt buffers , these globular chromatin units unfold into chains of7-12 nucleosomes. The results support the concept that chromatin is arranged , under physiological ion concentrations as they are present in the nucleus , in supranucleosomal units of globular morphology. 1980 urn:nbn:de:bvb:20-opus-39671 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3364 Wissenschaftlicher Artikel Franke, Werner W.; Kartenbeck, Jürgen; Krien, S.; VanderWoude, W. J.; Scheer, Ulrich; Morré, D. J. Inter- and intracisternal elements of the Golgi apparatus: A system of membrane-to-membrane cross-links Electron opaque cross-bridge structures span the inter- and intracisternal spaces and provide membrane-to-membrane connections between adjacent cisternae of dictyosomes of pollen tubes of Clivia and Lilium. Additionally, the classic intercisternal rods, characteristic of intercisternal regions near the maturing face of dictyosomes, are connected with the adjacent membranes through similar cross-bridge elements. We suggest that these structural links are responsible for maintaining the flattened appearance of the central parts of Golgi apparatus cisternae as well as for the coherence of cisternae within the stack. Observations on other plant (e.g. microsporocytes of Canna) and animal cells (e.g. rodent liver and hepatoma cells, newt spermatocytes) show that such an array of membrane cross-links is a universal feature of Golgi apparatus architecture. The cross-bridges appear as part of the complex "zone of exclusion" which surrounds dictyosomes, entire Golgi apparatus and Golgi apparatus equivalents in a variety of cell types. 1972 urn:nbn:de:bvb:20-opus-39514 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3365 Wissenschaftlicher Artikel Scheer, Ulrich The ultrastructure of the nuclear envelope of amphibian ooctyes: IV. On the chemical nature of the nuclear pore complex material In order to investigate the chemical composition of the nuclear pore complexes isolated nuclei from mature Xenopus laevis oocytes were manually fractioned into nucleo· plasmic aggregates and the nuclear envelopes. The whole isolation procedure takes no more than 60- 90 sec, and the pore complexes of the isolated envelopes are well preserved as demonstrated by electron microscopy. Minor nucleoplasmic and cytoplasmic contaminations associated with the isolated nuclear envelopes were determined with electron microscopic morphometry and were found to be quantitatively negligible as far as their mass and nucleic acid content is concerned. The RNA content of the fractions was determined by direct phosphorus analysis after differential alkaline hydrolysis. Approximately 9% of the total nuclear RNA of the mature Xenopus egg was found to be attached to the nuclear envelope. The nonmembranous elements of one pore complex contain 0.41 X 10- 16 g RNA. This value agrees well with the content estimated from morphometric data. The RNA package density in the pore complexes (270 X 10- 15 g/fJ-3) is compared with the nucleolar, nucleoplasmic and cytoplasmic RNA concentration and is discussed in context with the importance of the pore complexes for the nucleo-cytoplasmic transport of RNA-containing macromolecules. Additionally, the results of the chemical analyses as well as of the 3H-actinomycin D autoradiography and of the nucleoprotein staining method of Bernhard (1969) speak against the occurence of considerable amounts of DNA in the nuclear pore complex structures. 1972 urn:nbn:de:bvb:20-opus-39500 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3366 Wissenschaftlicher Artikel Franke, Werner W.; Scheer, Ulrich; Herth, Werner Cytology, general and molecular cytology The present article had originally been conceived as a review on endomembranes, the plasma membrane, and the major product of membrane-bound activities, the cell wall material. However, limitations of space and the cascading number of pertinent literature articles made it necessary to confine this to one group of membranes and one type of cell wall components. Therefore, we shall begin our survey on the biochemical and cytological aspects of membranes by a review of the class of the pore complex bearing endomembranes, i.e. the nuclear envelope and the annulate lamellae (AL). Next year the membranes of the endoplasmic reticulum and the dictyosomes will be dealt with in conjunction with a discussion of the various intracellular vesicles, the tonoplast and the plasmalemma. 1974 urn:nbn:de:bvb:20-opus-39499 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3367 Konferenzveröffentlichung Franke, Werner W.; Zentgraf, Hanswalter; Scheer, Ulrich Supranucleosomal and non-nucleosomal chromatin configurations A significant contribution to the understanding of chromatin organization was the d iscovery of the nucleosome as a globular repeating unit of the package of DNA (Hewish and Burgoyne, 1973; Woodcock, 1973; Kornberg, 1974; Olins and Olins, 1974; for review see Oudet et al., 1978 a) . In accord with the original definition and in ag reement with most workers in this field of research we identify a nucleosome as a spheric alor slightly oblate gr anular particle 10-13 nm in diameter, containing about 200 base pairs of DNA and two of each of the four his tones H2a, H2b, H3 and H4. It is this structure in which the bulk of the nuclear chroma tin is organized in most eukaryotic cells, with the exception of the dinofl age llates (Rae and Steele, 1977; dinofl agellate DNA, however, c an be packed into nucleosoma l structures in vitro by addition of the appropriate amounts of histones;the same reference). Although it seems clear from the work reported that condensed and transcriptiona lly inactive chroma tin is contained in nucleosomes as the principle for first order p acking of DNA there are two important questions onto which we are focusing in the present study: ( i ) What is the higher order of p a cking present in - and perhaps typical-of - the condensed sta te of chromatin, and (ii) what is the specific form of arrangement of transcriptionally a ctive chromatin? 1978 urn:nbn:de:bvb:20-opus-39447 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3368 Konferenzveröffentlichung Scheer, Ulrich Electron microscopic analysis of chromatin and gene expression No abstract available 1982 urn:nbn:de:bvb:20-opus-39456 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3371 Wissenschaftlicher Artikel Knecht, Sigrid; Scheer, Ulrich Lautäußerung und Verhalten des Azoren-Buchfinken (Fringilla coelebs moreletti Pucheran) Einleitung und Methode S. 155. - Brutbiologie S. 155. - Motivgesang S. 157. - Sozialruf (Social Call) S. 161. - Entwicklung des Sozialrufs S. 164. - Brumimmungsruf (Regenruf) S. 165. - Flugruf S. 166. - Alarmruf eines Jungvogels S. 167. - Bestimmung der ReviergroBe S. 167. - Zusammenfassung S. 168. - Summary S. 168. - Literaturverzeichnis S. 169. Es wird untersucht, ob die Azoren-Buchfinken "Rassengesang" und "Rassenrufe" haben. Gesange und Rufe wurden auf Tonband aufgenommen und klangspek trogra phiert. Motivgesang. Jedes cJ beherrscht 2-6 verschiedene Gesangsformen, wobei stets eine "Alltagsform" mit der stark vereinfachten Phrase di-djah endigt. Die anderen, weniger haufigeren Gesangsformen ("Sonntagsformen") zeigen eine besser ausgearbeitete Endphrase, die jedoch nie so kompliziert wie bei kontinentalen Buchfinken ist. In Gebieten, in denen sich bevorzugt Kanarienvogel aufhalten, konnen Buchfinken Gesangselemente iibernehmen. Sozialruf. Das kontinentale pink ist auf alIen Azoreninseln durch ga ersetzt, so daB man von einem Rassenruf sprechen kann. Er ist mit starker Aggressionsneigung verkniipft. Der Sozialruf zeigt einen weiten Frequenzumfang, hervorgerufen durch mehrere simultane Noten. Brutstimmungsruf (Regenruf). Eine Anzahl verschiedener Rufe wurde spektrographiert. Vom cJ ist er bei maBiger Gefahr, aber auch spontan (30-70 Rufe/Min.) zu horen. Flugruf. Er scheint mit dem Flugruf der Nominatform identisch zu sein. Bestimmung der Reviergrope. Ein cJ wurde innerhalb seines Reviers an die "akustische Leine" genommen und bis zu den Reviergrenzen gezogen. Verhalten und LautauBerung anderten sich in Abhangigkeit von der jeweiligen Entfernung bis zur Reviergrenze. 1968 urn:nbn:de:bvb:20-opus-39479 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3372 Review Scheer, Ulrich; Benavente, Ricardo Functional and dynamic aspects of the mammalian nucleolus Nucleoli are the sites of ribosome biogenesis. Transcription of the ribosomal RNA genes as well as processing and initial packaging of their transcripts with ribosomal and non-ribosomal proteins all occur within the nucleolus in an ordered manner and under defined topological conditions. Components of the nucleolus have been localized by immunocytochemistry and their functional aspects investigated by microinjection of antibodies directed against the enzyme responsible for rDNA transcription, RNA polymerase I. The role of nascent transcripts in postmitotic formation of nucleoli will be discussed. 1990 urn:nbn:de:bvb:20-opus-34269 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3373 Konferenzveröffentlichung Dabauvalle, M.-C.; Wilken, N.; Ewald, A.; Kuhbier, A.; Senécal, J.-L.; Scheer, Ulrich Nuclear pore complex structure analyzed by immunogold EM with human autoantibodies No abstract available 1994 urn:nbn:de:bvb:20-opus-39439 Theodor-Boveri-Institut für Biowissenschaften OPUS4-2635 Wissenschaftlicher Artikel Scheer, Ulrich; Weisenberger, Dieter The nucleolus No abstract available 1994 urn:nbn:de:bvb:20-opus-32037 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3073 Konferenzveröffentlichung Scheer, Ulrich; Rose, Kathleen M. Localization of RNA polymerase I in interphase cells and mitotic chromosomes by light and electron microscopic immunocytochemistry Rabbit antibodies to RNA polymerase I from a rat hepatoma have been used to localize the enzyme in a variety of cells at the light and electron microscopic level. In interphase cells the immunofluorescence pattern indicated that polymerase I is contained exclusively within the nucleolus. That this fluorescence, which appeared punctated rather than uniform, represented transcriptional complexes of RNA polymerase I and rRNA genes was suggested by the observation that it was enhanced in regenerating liver and in a hepatoma and was markedly diminished in cells treated with actinomycin D. Electron microscopic immunolocalization using gold-coupled second antibodies showed that transcribed rRNA genes are located in, and probably confined to, the fibrillar centers of the nucleolus. In contrast, the surrounding dense fibrillar component, previously thought to be the site of nascent prerRNA, did not contain detectable amounts of polymerase I. During mitosis, polymerase I molecules were detected by immunofluorescence microscopy at the chromosomal nucleolus organizer region, indicating that a considerable quantity of the enzyme remains bound to the rRNA genes. From this we conclude that rRNA genes loaded with polymerase I molecules are transmitted from one cell generation to the next one and that factors other than the polymerase itself are involved in the modulation of transcription of DNA containing rRNA genes during the cell cycle. 1984 urn:nbn:de:bvb:20-opus-33223 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3087 Wissenschaftlicher Artikel Zentgraf, Hanswalter; Trendelenburg, Michael F.; Spring, Herbert; Scheer, Ulrich; Franke, Werner W.; Müller, Ulrike; Drury, Kenneth C.; Rungger, Duri Mitochondrial DNA arranged into chromatin-like structures after injection into amphibian oocyte nuclei Purified mitochondrial DNA (mitDNA) from ovaries ofXenopus lae vis was injected into the nuclei (germinal vesicles) of large viteUogenic oocytes of the same organism and examined by electron microscopy ofthe spread nuclear contents. Normally located nuclei of untreated oocytes as weil as peripherally translocated nuclei of centrifuged oocytes were used. In addition, oocyte nuclei isolated and incubated under liquid paraffin oil were injected with DNA. The integrity oftranscriptional structures of endogenous chromosomal (Iampbrush chromosomes) and extrachromosomal (nucleoli) genes of the injected nuclei was demonstrated. Microinjected mitDN A was identified as circles of chromatin exhibiting polynucleosome-like organization and a me an contour length of 2.6 J.Lm, corresponding to a compaction ratio of the mitDN A of about 2 : I. This DNA packing ratio is similar to that observed after preparation of various kinds of native chromatin in low salt buffers. The chromatin circles formed from injected mitDNA only very rarely exhibited lateral fibrils suggestive of transcriptional activity. These results suggest that purified mitDNA can be transformed to normally structured chromatin when exposed to oocyte nuclear contents but is rarely , if at all , transcribed in this form and in this environment. 1979 urn:nbn:de:bvb:20-opus-33174 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3088 Wissenschaftlicher Artikel Scheer, Ulrich; Hügle, Barbara; Hazan, Rachel; Rose, Kathleen M. Drug-induced dispersal of transcribed rRNA genes and transcriptional products: Immunolocalization and silver staining of different nucleolar components in rat cells treated with 5,6-dichloro-1-Beta-D-ribofuranosylbenzimidazole Upon incubation of cultured rat cells with the adenosine analogue 5,6-dichloro-l-β- D-ribofuranosylbenzimidazole (DRB), nucleoli reversibly dissociate into their substructures, disperse throughout the nuclear interior, and form nucleolar "necklaces". We have used this experimental system, which does not inhibit transcription of the rRNA genes, to study by immunocytochemistry the distribution of active rRNA genes and their transcriptional products during nucleolar dispersal and recovery to normal morphology. Antibodies to RNA polymerase I allow detection of template-engaged polymerase, and monoclonal antibodies to a ribosomal protein (S 1) of the small ribosomal subunit permit localization of nucleolar preribosomal particles. The results show that, under the action of DRB transcribed rRNA, genes spread throughout the nucleoplasm and finally appear in the form of several rows, each containing several (up to 30) granules positive for RNA polymerase land argyrophilic proteins. Nucleolar material containing preribosomal particles also appears in granular structures spread over the nucleoplasm but its distribution is distinct from that of rRNA gene-containing granules. We conclude that, although transcriptional units and preribosomal particles are both redistributed in response to DRB, these entities retain their individuality as functionally defined subunits. We further propose that each RNA polymerase-positive granular unit represents a single transcription unit and that each continuous array of granules ("string of nucleolar beads") reflects the linear distribution of rRNA genes along a nucleolar organizer region. Based on the total number of polymerase I-positive granules we estimate that a minimum of 60 rRNA genes are active during interphase of DRB-treated rat cells. 1984 urn:nbn:de:bvb:20-opus-33216 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3089 Wissenschaftlicher Artikel Scheer, Ulrich; Lanfranchi, Gerolamo; Rose, Kathleen M.; Franke, Werner W.; Ringertz, Nils R. Migration of rat RNA polymerase I into chick erythrocyte nuclei undergoing reactivation in chick-rat heterokaryons Transcriptionally inactive chick erythrocyte nudei were reactivated by Sendai virusinduced fusion of erythrocytes with rat L6j1 myoblasts. We used antibodies to trace the appearance of a specific protein engaged in transcription of a defined dass of genes, those coding for rRNA, during reactivation. Using immunofluorescence microscopy, we found increasing amounts of rat RNA polymerase I to appear, during a certain period of time after fusion, in the reforming nudeoli of the chick nudei. Amounts of rat RNA polymerase I sufficient to be detected by immunofluorescence microscopy had accumulated in the newly developed chick nudeoli 72- 190 h after fusion was initiated. This time interval coincides with the time when chick rRNA synthesis can first be detected. The results raise the possibility that during these stages of the reactivation process chick rRNA genes are transcribed by heterologous RNA polymerase I moleeules of rat origin. 1983 urn:nbn:de:bvb:20-opus-33232 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3090 Konferenzveröffentlichung Zentgraf, Hanswalter; Scheer, Ulrich; Franke, Werner W. On the existence of arrested transcriptional machinery in late stages of avian erythropoiesis No abstract available 1976 urn:nbn:de:bvb:20-opus-33696 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3091 Konferenzveröffentlichung Franke, Werner W.; Scheer, Ulrich Pathways of nucleocytoplasmic translocation of ribonucleoproteins No abstract available 1974 urn:nbn:de:bvb:20-opus-33832 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3092 Konferenzveröffentlichung Trendelenburg, M. F.; Franke, Werner W.; Spring, H.; Scheer, Ulrich Ultrastructure of transcription in the nucleoli of the green algae Acetabularia major and A. mediterranea No abstract available 1975 urn:nbn:de:bvb:20-opus-33779 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3093 Konferenzveröffentlichung Franke, Werner W.; Scheer, Ulrich Biochemical and structural aspects of nucleocytoplasmic transfer of ribonucleoproteins at the nuclear envelope level: facts and theses No abstract available 1975 urn:nbn:de:bvb:20-opus-33766 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3094 Konferenzveröffentlichung Scheer, Ulrich; Trendelenburg, M. F.; Franke, Werner W. Regulation of transcription of ribosomal RNA genes during amphibian oogenesis No abstract available 1976 urn:nbn:de:bvb:20-opus-33700 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3095 Wissenschaftlicher Artikel Dabauvalle, Marie-Christine; Schulz, Barbara; Scheer, Ulrich; Peters, Reiner Inhibition of nuclear accumulation of karyophilic proteins in living cells by microinjection of the lectin wheat germ agglutinin No abstract available 1988 urn:nbn:de:bvb:20-opus-34288 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3096 Wissenschaftlicher Artikel Rungger, M.; Crippa, M.; Trendelenburg, M. F.; Scheer, Ulrich; Franke, Werner W. Visualization of rDNA spacer transcription in Xenopus oocytes treated with fluorouridine Under the intluence of 5-tluoro-uridine, the ultrastructure of the rDNA transcription units in Xenopus oocytes is altered. Whereas part of the matrix units maintains anormal aspect or shows various degrees of inhibition, in a strong proportion of the transcription units the alternating pattern of matrix units and fibril-free spacer regions is no longer recognized. Transcriptional complexes are found along the entire DNP axis, including the regions of the spacers. These observations support biochemical data on transcription in rDNA spacer region. 1978 urn:nbn:de:bvb:20-opus-33082 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3097 Wissenschaftlicher Artikel Scheer, Ulrich; Sommerville, John Sizes of chromosome loops and hnRNA molecules in oocytes of amphibia of different genome sizes The lengths of lampbrush chromosome loops and their tran scription units show a positive correlation with genome size in oocytes of amphibia with different C values. However, there is no such correlation with contour lengths of hnRNA molecu les isolated from these oocytes. These results indi cate th at more ON A sequences are transcribed in amphibia of higher C value , but that processing of RNA transc ripts occurs while they are still attached to the chromosomes as nascent ribonucleoprotein fibrils. 1982 urn:nbn:de:bvb:20-opus-33094 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3098 Wissenschaftlicher Artikel Krohne, Georg; Franke, Werner W.; Scheer, Ulrich The major polypeptides of the nuclear pore complex Nuclear envelopes of maturing oocytes of various amphibia contain an unusually high number of pore complexes in very close packing. Consequently, nuclear envelopes , which can be manually isolated in great purity, provide a remarkable enrichment of nuclear pore complex material, relative to membranous and other interporous structures. When the polypeptides of nuclear envelopes isolated from oocytes of Xenopl/s la evis and Triturus alpestris are examined by gel electrophoresis, visualized either by staining with Coomassie blue or by radiotluorography after in vitro reaction with [3H]dansyl chloride , a characteristic pattern is obtained (10 major and 15 minor bands). This polypeptide pattern is radically different from that of the nuclear contents isolated from the same cell. Extraction of the nuclear envelope with high salt concentrations and moderateIy ac tive detergents such as Triton X- 100 results in the removal of membrane material but leaves most of the non-membranous structure of the pore complexes. The dry weight of the pore complex (about 0.2 femtograms) remains essentially unchanged during such extractions as measured by quantitative electron microscopy . The extracted preparations which are highly enriched in nuclear pore complex material contain only two major polypeptide components with apparent molecular weights of 150000 and 73000. Components of such an electrophoretic mobility are not present as major bands , if at all , in nuclear contents extracted in the same way. lt is concluded that these two polypeptides are the major constituent protein(s) of the oocyte nuclear pore complex and are specific for this structure. When nuclear envelopes are isolated from rat liver and extracted with high salt buffers and Triton X- 100 similar bands are predominant, but two additional major components of molecular weights of 78000 and 66000 are also recognized. When the rat liver nuclear membranes are further subfractionated material enriched in the 66000 molecular weight component can be separated from the membrane material, indicating that this is relatively loosely associated material , probably a part of the nuclear matrix . The results suggest that the nuclear pore complex is not only a characteristic ubiquitous structure but also contains similar, if not identical , skeletal proteins that are remarkably re sistant to drastic changes of ionic strength as weil as to treatments with detergents and thiol reagents. 1978 urn:nbn:de:bvb:20-opus-33078 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3058 Wissenschaftlicher Artikel Hadjiolova, Krassimira; Rose, Kathleen M.; Scheer, Ulrich Immunolocalization of nucleolar proteins after D-galactosamine-induced inhibition of transcription in rat hepatocytes No abstract available 1986 urn:nbn:de:bvb:20-opus-33205 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3059 Wissenschaftlicher Artikel Moreno-Diaz de la Espina, Susana; Franke, Werner W.; Krohne, Georg; Trendelenburg, Michael F.; Grund, Christine; Scheer, Ulrich Medusoid fibril bodies: a novel type of nuclear filament of diameter 8 to 12 nm with periodic ultrastructure demonstrated in oocytes of Xenopus laevis No abstract available 1982 urn:nbn:de:bvb:20-opus-34116 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3227 Wissenschaftlicher Artikel Franke, Werner W.; Scheer, Ulrich The ultrastructure of the nuclear envelope of amphibian oocytes: a reinvestigation. I. The mature oocyte 1 n order to review the contradictory statements on the ultrast ructure of the nuclear envelope, a study was undertaken combining section and negat ive stai ning electron microscopy on manually isolated oocyte nuclei and nuclear envelopes from six amphibian species including Anura as well as Urodela. The a ppeara nce of the negatively stained iso lated nuclear envelopes is described in deta il and the dependence on the preparation co nditions used is emphas ized . Pore complex structures such as pore perimeter, central granule, an nul ar components, interna l fibrils, and annu lus-attached fibrils could be identified by both techniques, negat ive staining and sect ions. Comparative studies show that no marked diffe rences ex ist in the structural data of the nuclear envelope among the investigated amphibians and the significance of the structural components is discussed. A model of the nuclea r pore complex based on the findings of the present investigation is prese nted. 1970 urn:nbn:de:bvb:20-opus-32098 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3104 Wissenschaftlicher Artikel Zentgraf, H.; Müller, U.; Scheer, Ulrich; Franke, W. W. Evidence for the existence of globular units in the supranucleosomal organization of chromatin No abstract available 1981 urn:nbn:de:bvb:20-opus-34123 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3105 Wissenschaftlicher Artikel Scheer, Ulrich; Trendelenburg, Michael F.; Krohne, Georg; Franke, Werner W. Lengths and patterns of transcriptional units in the amplified nucleoli of oocytes of Xenopus laevis Transcriptionally active chromatin from peripheral amplified nuc1eoli of lampbrush-chromosome stage oocytes of Xenopus laevis was dispersed and spread in various solutions of low salt concentrations (incIuding some with additions of detergents) and examined by electron microscopy. Nucleolar material from oocytes of animals with normal (2-nu) and mutant (I-nu) genetical constitution of nucleolus organizers was compared. Histograms showing the distributions of the lengths of matrix units, apparent spacer intercepts, and the total repeating units of the rDNA containing chromatin axes revealed a significant degree of heterogeneity, with indications of subclasses and predominant repeat unit size c1asses of 3.3 and 3.8 11m length. The correspondence of matrix unit length to the molecular weight of the first stable product of rDNA transcription was studied using gel electrophoresis of labelIed pre-rRNA under non-denaturing and denaturing conditions. Evaluations of individual strands of nucleolar chromatin furt her demonstrated the existence of both (i) strands with obviously homogeneous repeating units and (ii) strands with intra-axial heterogeneity of rDNA subunits. " Preludecomplexes ", i.e. groups of transcriptional complexes in apparent spacer intercepts, were not infrequently noted. The data are compared with the measurements of lengths of repeating units in fragments of rDNA obtained by digestion with EcoRI endonuclease as described by Morrow et al. (1974) and Wellauer et al. (1974, 1976a, b). The results are discussed in relation to problems of variations in the modes of arrangement of the pre-rRNA genes, the state of packing of rDNA during transcription, and possible mechanisms of the amplification process. 1977 urn:nbn:de:bvb:20-opus-33069 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3106 Wissenschaftlicher Artikel Scheer, Ulrich; Zentgraf, Hanswalter Nucleosomal and supranucleosomal organization of transcriptionally inactive rDNA circles in Dytiscus oocytes Oocytes of the water beetle, Dytiscus marginalis, contain large amounts of rDNA most of which is present in the form of rings containing one or several pre-rRNA genes. Electron microscopy of spread preparations of vitellogenic oocytes has shown that the rDNA is extended in chromatin rings with transcribed pre- rRNA genes and is not packed into nucleosomes (Trendelenburg eta!. , 1976). When similar preparations are made from previtellogenic ooytes in which a large proportion of the nuc1eolar chromatin is transcriptionally inactive, a different morphological form of this chromatin is recognized. In contrast to the transcribed chromatin rings the inactive nucleolar chromatin circles show the characteristic beaded configuration, indicative of nucleosomal packing. Nuc1eosomal packing is also indicated by the comparison of the lengths of these chromatin rings with both iso lated rDNA circ1es and transcribed chromatin rings. In addition, these inactive nuc1eofilaments often appear to be compacted into globular higher order structures of diameters from 21 to 34nm, each composed of an aggregate of 6-9 nuc1eosomes. While the estimated reduction of the overall length of rDNA, as seen in our preparations, is, on the average, only 2.2 - 2.4 fold in the nuc1eosomal state it is 10- 13 fold when supranuc1eosomal globules are present. These data show that the extrachromosomal rDNA of these oocytes goes through a cycle of condensation and extensio n, as a function of the specific transcriptional activity, and that the beaded state described here is exc1usively found in the non-transcribed state. 1978 urn:nbn:de:bvb:20-opus-33188 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3123 Wissenschaftlicher Artikel Trendelenburg, Michael F.; Scheer, Ulrich; Zentgraf, Hanswalter; Franke, Werner W. Heterogeneity of spacer lengths in circles of amplified ribosomal DNA of two insect species, Dytiscus marginalis and Acheta domesticus No abstract available 1976 urn:nbn:de:bvb:20-opus-33055 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3125 Wissenschaftlicher Artikel Bona, Marion; Scheer, Ulrich; Bautz, Ekkehard K. F. Antibodies to RNA polymerase II (B) inhibit transcription in lampbrush chromosomes after microinjection into living amphibian oocytes Antibodies directed against RNA polymerase II (B) from Drosophila melanogaster were obtained from rabbit sera and, as monoclonal immunoglobulins, from mouse hybridomas and shown to cross-react with the amphibian enzyme protein. Localization by indirect immunofluorescence microscopy revealed the association of this enzyme with chromatin of interphase nuclei of amphibian cells and its absence in nucleoli. Purified immunoglobulins were microinjected in to nuclei ofliving vitellogenic oocytes of Ple1lrodeles waltlii and X enopus laevis and their effects on transcriptional processes were monitored by biochemical and light and electron microscopic stud ies. RNA polymerase II antibodies from rabbit sera caused a rapid and almost complete release of nascent transcripts from the chromatin axis of the loops of lampbrush chromosomes, followed by collapse of the loops and their retraction on the main chromosome axis. Monoclonal murine antibodies to the Iarge RNA polymerase II subunits also inhibited transcription in chromosome Ioops but appeared to inhibit initiation rather than elongation events. Activities of class land III RNA polymerases were not significantly affected by injection of antibodies to polymerase II, indicating immunological differences between the three RNA polymerases. The potential value of the in vitro test system described , as a very sensitive assay for detecting proteins involved in transcription in living cells, is discussed. 1 1981 urn:nbn:de:bvb:20-opus-33128 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3126 Wissenschaftlicher Artikel Franke, Werner W.; Scheer, Ulrich; Krohne, Georg; Jarasch, Ernst-Dieter The nuclear envelope and the architecture of the nuclear periphery No abstract available 1981 urn:nbn:de:bvb:20-opus-33108 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3127 Wissenschaftlicher Artikel Franke, Werner W.; Kleinschmidt, Jürgen A.; Spring, Herbert; Krohne, Georg; Grund, Christine; Trendelenburg, Michael F.; Stöhr, Michael; Scheer, Ulrich A nucleolar skeleton of protein filaments demonstrated in amplified nucleoli of Xenopus laevis The amplified, extrachromosomal nucleoli of Xenopus oocytes contain a meshwork of -4-nm-thick filaments, which are densely coiled into higher-order fibrils of diameter 30-40 nm and are resistant to treatment with high- and low-salt concentrations, nucleases (DNase I, pancreatic RNase, micrococcal nuclease), sulfhydryl agents, and various nonionic detergents. This filamentous "skeleton" has been prepared from manually isolated nuclear contents and nucleoli as weil as from nucleoli isolated by fluorescence-activated particle sorting. The nucleolar skeletons are observed in light and electron microscopy and are characterized by ravels of filaments that are especially densely packed in the nucleolar cortex. DNA as weil as RNA are not constituents of this structure, and precursors to ribosomal RNAs are completely removed from the extraction-resistant filaments by treatment with high-salt buffer or RN ase. Fractions of isolated nucleolar skeletons show specific enrichment of an acidic major protein of 145,000 mol wt and an apparent pi value of -6.15, accompanied in some preparations by various amounts of minor proteins. The demonstration of this skeletal structure in "free" extrachromosomal nucleoli excludes the problem of contaminations by nonnucleolar material such as perinucleolar heterochromatin normally encountered in studies of nucleoli from somatic cells. It is suggested that this insoluble protein filament complex forms a skeleton specific to the nucleolus proper that is different from other extraction-resistant components of the nucleus such as matrix and lamina and is involved in the spatial organization of the nucleolar chromatin and its transcriptional products. In studies of the organization of the interphase nucleus, considerable progress has been made in the elucidation of the arrangement of chromatin components and transcriptional products. However, relatively little is known about the composition and function of another category of nuclear structures, the nonnucleoproteinaceous architectural components that are insoluble in solutions of low and high ionic strength, despite numerous studies dedicated to this problem. Such structures include (a) the nuclear envelope and its pore complexes (I, 15, 18, 23, 37, 41), (b) a peripheral layer of insoluble protein ("lamina"; I, 15, 22, 23, 59), (e) certain skeletal proteins related to the chromosome "scaffold" described by Laemmli and coworkers (see references 2 and 3), and (d) ill-defined tangles of fibrillar structures of the nuclear interior that are collectively described as residual "matrix" (6, 21 ; for reviews, see references THE JOURNAL OF CEll BrOlOGY . VOlUME 90 AUGUST 1981 289-299 © The RockefeIler University Press · 0021 -9525/ 81 / 08/ 0289/ 11 $1 .00 4 and 12). The latter, preparatively 1981 urn:nbn:de:bvb:20-opus-33130 Theodor-Boveri-Institut für Biowissenschaften OPUS4-3128 Wissenschaftlicher Artikel Scheer, Ulrich Identification of a novel class of tandemly repeated genes transcribed on lampbrush chromosomes of Pleurodeles waltlii Electron microscope preparations of lampbrush chromosomes from oocytes of Pleurodeles waltl;; have revealed a new class of tandemly repeated genes. These genes are highly active, as judged by the close spacing of nascent transcripts. They occur in clusters of >100 copies and are transcribed in units containing roughly 940 base pairs of DNA that are separated by nontranscribed spacers of an estimated DNA content of 2,410 base pairs. The size and the pattern of arrangement of these transcription units can not be correlated with any of the repetitious genes so far described. 1981 urn:nbn:de:bvb:20-opus-33153 Theodor-Boveri-Institut für Biowissenschaften