@article{TzagoloffMacinoSebald1979,
author = {Tzagoloff, A. and Macino, G. and Sebald, Walter},
title = {Mitochondrial genes and translation products},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-47408},
year = {1979},
abstract = {No abstract available},
subject = {Biochemie},
language = {en}
}
@article{SebaldWernerWeiss1979,
author = {Sebald, Walter and Werner, S and Weiss, H},
title = {Biogenesis of mitochondrial membrane proteins in Neurospora crassa},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-82055},
year = {1979},
abstract = {no abstract available},
subject = {Biochemie},
language = {en}
}
@article{SebaldWild1979,
author = {Sebald, Walter and Wild, G.},
title = {Mitochondrial ATPase complex from Neurospora crassa},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-82065},
year = {1979},
abstract = {The A TPase eomplex has been isolated from mitoehondria of N eurospora crassa by immunologieal teehniques. The protein ean be obtained rapidly and qua ntitatively in high purity by miero- or large-seale immunopreeipitation. Immunopreeipitation has been applied to labeled and doubly labeled mitoehondrial proteins in order to investigate the number and moleeular weights of subunit polypeptides , the site of synthesis of subunit polypeptides, and the dieycIohexyIcarbodiimide-binding protein . The A TPase complex obtained by large-seale immunopreeipitation has been used as starting ma terial for the isolation of hydrophobie polypeptides.},
subject = {Biochemie},
language = {en}
}
@article{SebaldNeupertWeiss1979,
author = {Sebald, Walter and Neupert, W. and Weiss, H.},
title = {Preparation of Neurospora crassa mitochondria},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-82070},
year = {1979},
abstract = {The fungus Neurospora crassa represents a eukaryotic cell with high biosynthetic activities. Cell mass doubles in 2-4 hr during expone ntial growth , even in simple salt media with sucrose as the sole carbon source. The microorgani sm forms a mycelium of long hyphae durlng vegetative growth . The mitochondria can be isolated under relatively gentle condi tions since a few breaks in the threadlike hyphae are sufficient to cause the outflow of the organelles. This article describes two methods for the physical disruption of the hyphae : (I) The cell s are opened in a grind mill between two rotating corundum di sks. This is a continuous and fast procedure and allows large- and small-scale preparations of mitochondria. (2) Hyphae are ground with sand in a mortar and pestle. This procedure can be applied to microscale preparations of mitochondria starting with minute amounts of cells. Other procedures for the isolation of Neurospora mitochondria after the physical di sruption or the enzymatic degradation of the cell wall have been described elsewhere},
subject = {Biochemie},
language = {en}
}
@article{HoppeSebald1980,
author = {Hoppe, J. and Sebald, Walter},
title = {Amino acid sequence of the proteolipid subunit of the proton-translocating ATPase complex from the thermophilic bacterium PS-3},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-62754},
year = {1980},
abstract = {No abstract available},
subject = {Biochemie},
language = {en}
}
@article{HoppeSchairerSebald1980,
author = {Hoppe, J. and Schairer, H. U. and Sebald, Walter},
title = {The proteolipid of a mutant ATPase from Escherichia coli defective in H\(^+\)-conduction contains a glycine instead of the carbodiimide-reactive aspartyl residue},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-62769},
year = {1980},
abstract = {No abstract available},
subject = {Biochemie},
language = {en}
}
@article{HoppeSchairerSebald1980,
author = {Hoppe, J. and Schairer, HU and Sebald, Walter},
title = {Identification of amino-acid substitutions in the proteolipid subunit of the ATP synthase from dicyclohexylcarbodiimide-resistant mutants of Escherichia coli},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-47374},
year = {1980},
abstract = {The amino acid sequence of the proteolipid subunit of the A TP synthase was analyzed in six mutant strains from Escherichia coli K 12, selected for their increased resistance towards the inhibitor N,N'-dicyclohexylcarbodiimide. All six inhibitor-resistant mutants were found to be altered at the same position of the proteolipid, namely at the isoleucine at residue 28. Two substitutions could be identified. In type I this residue was substituted by a valine resulting in a moderate decrease in sensitivity to dicyclohexylcarbodiimide. Type II contained a threonine residue at this position. Here a strong resistance was observed. These two amino acid substitutions did not influence functional properties of the ATPase complex. ATPase as well as A TP-dependent proton-translocating activities of mutant membranes were indistinguishable from the wild type. At elevated concentrations, dicyclohexylcarbodiimide still bound specifically to the aspartic acid at residue 61 of the mutant proteolipid as in the wild type, and thereby inhibited the activity of the ATPase complex. It is suggested that the residue 28 substituted in the resistant mutants interacts with dicyclohexylcarbodiimide during the reactions leading to the covalent attachment of the inhibitor to the aspartic acid at residue 61. This could indicate that these two residues are in close vicinity and would thus provide a first hint on the functional conformation of the proteolipid. Its polypeptide chain would have to fold back to bring together these two residues separated by a segment of 32 residues.},
subject = {Biochemie},
language = {en}
}
@article{Kreft1980,
author = {Kreft, J{\"u}rgen},
title = {Reovirus-specific messenger ribonucleoprotein particles from Hela cells},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-47028},
year = {1980},
abstract = {When reovirus-infected Hela cells are incubated at 43°C virus-specific messenger RNA is released ~rom the polysomes. It accumulates free in the cytoplasm as messenger ribonucleoprotem partIcles (mRNPs). The:e part~cles have a sedimentati~n rate of about 50S and a buoyant densIty m CsCI of 1.42 g/cm . ReovIrus mRNPs contam, beSIdes all three size classes of reovirus messenger RNA, the same spectrum of proteins found in the polysomal mRNPs from uninfected cells, plus t~o addi~ional pr?teins with molecular masses of 7000~ d and 110000 d, respectively. Electron mIcroscoPIc exammatlOn of the reovIrus mRNP fractIOn reveals specific Y-shaped structures wIth a total mean length ofO.5Ilm.},
language = {en}
}
@article{ScheerSommervilleMueller1980,
author = {Scheer, Ulrich and Sommerville, John and M{\"u}ller, Ulrike},
title = {DNA is assembled into globular supranucleosomal chromatin structures by nuclear contents of amphibian oocytes},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-39671},
year = {1980},
abstract = {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.},
language = {en}
}
@article{Scheer1980,
author = {Scheer, Ulrich},
title = {Structural organization of spacer chromatin between transcribed ribosomal RNA genes in amphibian oocytes},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-41057},
year = {1980},
abstract = {Transcribed nucleolar chomatin, including the spacer regions interspersed between the rRNA genes, is different from the bulk of nontranscribed chromatin in that the DNA of these regions appears to be in an extended (B) conformation when examined by electron microscopy. The possibility that this may reflect artificial unfolding of nucleosomes during incubation in very low salt buffers as routinely used in such spread preparations has been examined by studying the influence of various ion concentrations on nucleolar chromatin structure. Amplified nucleolar chromatin of amphibian oocytes (Xenopus laevis, Pleurodeles waltlii, Triturus cristatus) was spread in various concentrations of NaCl (range 0 to 20 mM). Below 1 mM salt spacer chromatin frequently revealed a variable number of irregularly shaped beads, whereas above this concentration the chromatin axis appeared uniformly smooth. At all salt concentrations studied, however, the length distribution of spacer and gene regions was identical. Preparations fixed with glutaraldehyde instead of formaldehyde, or unftxed preparations, were indistinguishable in this respect. The observations indicate that (i) rDNA spacer regions are not compacted into nucleosomal particles and into supranucleosomal structures when visualized at chromatin stabilizing salt concentrations (e.g., 20 mM NaCl), and (ii) spacer DNA is covered by a uniform layer of proteins of unknown nature which, at very low salt concentrations (below 1 mM NaCl), can artificially give rise to the appearance of small granular particles of approximately nucleosome-like sizes. These particles, however, are different from nucleosomes in that they do not foreshorten the associated spacer DNA. The data support the concept of an altered nucleohistone conformation not only in transcribed chromatin but also in the vicinity of transcriptional events.},
subject = {Cytologie},
language = {en}
}
@article{vonJagowSebald1980,
author = {von Jagow, Gerhard and Sebald, Walter},
title = {b-Type cytochromes},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-47383},
year = {1980},
abstract = {No abstract available},
subject = {Biochemie},
language = {en}
}
@article{SebaldMachleidtWachter1980,
author = {Sebald, Walter and Machleidt, Werner and Wachter, Elmar},
title = {N,N'-dicyclohexylcarbodiimide binds specifically to a single glutamyl residue of the proteolipid subunit of the mitochondrial adenosinetriphosphatases from Neurospora crassa and Saccharomyces cerevisiae},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-47394},
year = {1980},
abstract = {T~e N,N'-dicrclohexylcarbodiimide-binding proteolipid subumt of the mitochondrial adenosinetriphosphatases (ATP phosphohydrolase, EC 3.6.1.3) of Neurosporacrassa and Saccharomyces cerevisiae were purified from mitochondria incubated with the radioactively labeled inhibitor. The specifically labeled subunit was cleaved with cyanogen bromide and N-bromosuccinimide, and the resultant fragments were separated by gel chromatography in the presence of 80\% (vol/vol) formic acid. The N,N'-dicyclohexylcarbodiimide label was recovered in each organism exclusively in a 17-residue fragment. Further analysis by automated solid-phase Edman degrada.ti.on revealed tha~ the bound label was present at only one positIOn, correspondmg to a glutamyl residue. The NN'~ icyc~ohexyl~a~bodiiJ?1~de-'!l0dified glutamyl residue is the ~nly Id~ntIcal aCidic posItIon m both proteins and occurs in the middle of a hydrophobic sequence of about 25 residues.},
subject = {Dicyclohexylcarbodiimid},
language = {en}
}
@article{ScheerZentgrafSauer1981,
author = {Scheer, Ulrich and Zentgraf, Hanswalter and Sauer, Helmut W.},
title = {Different chromatin structures in Physarum polycephalum: a special form of transcriptionally active chromatin devoid of nucleosomal particles},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-33148},
year = {1981},
abstract = {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).},
language = {en}
}
@article{ScheerSommerville1981,
author = {Scheer, Ulrich and Sommerville, J.},
title = {Structural organization of nascent transcripts and hnRNA molecules in amphibian oocytes},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-39765},
year = {1981},
abstract = {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.},
language = {en}
}
@article{ZentgrafMuellerScheeretal.1981,
author = {Zentgraf, H. and M{\"u}ller, U. and Scheer, Ulrich and Franke, W. W.},
title = {Evidence for the existence of globular units in the supranucleosomal organization of chromatin},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-34123},
year = {1981},
abstract = {No abstract available},
language = {en}
}
@article{BonaScheerBautz1981,
author = {Bona, Marion and Scheer, Ulrich and Bautz, Ekkehard K. F.},
title = {Antibodies to RNA polymerase II (B) inhibit transcription in lampbrush chromosomes after microinjection into living amphibian oocytes},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-33128},
year = {1981},
abstract = {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},
language = {en}
}
@article{FrankeScheerKrohneetal.1981,
author = {Franke, Werner W. and Scheer, Ulrich and Krohne, Georg and Jarasch, Ernst-Dieter},
title = {The nuclear envelope and the architecture of the nuclear periphery},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-33108},
year = {1981},
abstract = {No abstract available},
language = {en}
}
@article{FrankeKleinschmidtSpringetal.1981,
author = {Franke, Werner W. and Kleinschmidt, J{\"u}rgen A. and Spring, Herbert and Krohne, Georg and Grund, Christine and Trendelenburg, Michael F. and St{\"o}hr, Michael and Scheer, Ulrich},
title = {A nucleolar skeleton of protein filaments demonstrated in amplified nucleoli of Xenopus laevis},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-33130},
year = {1981},
abstract = {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},
language = {en}
}
@article{Scheer1981,
author = {Scheer, Ulrich},
title = {Identification of a novel class of tandemly repeated genes transcribed on lampbrush chromosomes of Pleurodeles waltlii},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-33153},
year = {1981},
abstract = {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.},
language = {en}
}
@article{WernerSebald1981,
author = {Werner, S. and Sebald, Werner},
title = {Immunological techniques for studies on the biogenesis of mitochondrial membrane proteins},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-82044},
year = {1981},
abstract = {no abstract available},
subject = {Biochemie},
language = {en}
}
@article{SchairerHoppeSebaldetal.1982,
author = {Schairer, H. U. and Hoppe, J. and Sebald, Walter and Friedl, P.},
title = {Topological and functional aspects of the proton conductor, F\(_0\), of the Escherichia coli ATP-synthase},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-62721},
year = {1982},
abstract = {The isolated H\(^+\) conductor, F\(_0\) , of the Escherichia co1i ATP-synthase consists of three subunits, a, b, and c. H\(^+\) -permeable liposomes can be reconstit~ted with F\(_0\) and lipids; addition of F\(_1\)-ATPase reconstitutes a functional ATP-synthase. Mutants with altered or misslng F\(_0\) subunits are defective in H\(^+\) conduction. Thus, all three subunits are necessary for the expression of H\(^+\) conduction. The subunits a and b contain binding sites for F\(_1\)• Computer calculations, cross-links, membrane-permeating photo-reactive labels, and proteases were used to develop tentative structural models for the individual F\(_0\) subunits.},
subject = {Biochemie},
language = {en}
}
@article{SebaldFriedlSchaireretal.1982,
author = {Sebald, Walter and Friedl, P. and Schairer, H. U. and Hoppe, J.},
title = {Structure and genetics of the H\(^+\)-conducting F\(_0\) portion of the ATP synthase},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-62733},
year = {1982},
abstract = {The ATP synthase occurs in remarkably conserved form in procaryotic and eucaryotic cells. Thus, our present knowledge of ATP synthase is derived from sturlies of the enzyme from different organisms, each affering specific experimental possibilities. In recent tim es, research on the H\(^+\) -conducting F0 part of the ATP synthase has been greatly stimulated by two developments in the Escherichio coli system. Firstly, the purification and reconstitution of the whole ATP synthase as weil as the proton conductor Fa from E. coli have been achieved. These functionally active preparations are well defined in terms of subunit composition, similar to the thermophilic enzyme from PS-3 studied by Kagawa's group.u Secondly, the genetics and the molecular cloning of the genes of all the F\(_0\) subunits from E. coli yielded information on the function of subunit polypeptides and essential amino acid residues. Furthermore, the amino acid sequence of hydrophobic F\(_0\) subunits, which are difficult to analyze by protein-chemical techniques, could be derived from the nucleotide sequence of the genes. These achievements, which shall be briefly summarized in the next part of this communication, provide the framework to study specific aspects of the structure and function of the F\(_0\) subunits.},
subject = {Biochemie},
language = {en}
}
@article{ViebrockPerzSebald1982,
author = {Viebrock, A. and Perz, A. and Sebald, Walter},
title = {The imported preprotein of the proteolipid subunit of the mitochondrial ATP synthase from Neurospora crassa. Molecular cloning and sequencing of the mRNA},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-62742},
year = {1982},
abstract = {No abstract available},
subject = {Biochemie},
language = {en}
}
@article{SchartlBarnekowBaueretal.1982,
author = {Schartl, Manfred and Barnekow, A. and Bauer, H. and Anders, F.},
title = {Correlations of inheritance and expression between a tumor gene and the cellular homolog of the Rous sarcoma virus-transforming gene in Xiphophorus},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61937},
year = {1982},
abstract = {No abstract available},
subject = {Physiologische Chemie},
language = {en}
}
@article{BarnekowSchartlAndersetal.1982,
author = {Barnekow, A. and Schartl, Manfred and Anders, F. and Bauer, H.},
title = {Identification of a fish protein associated with a kinase activity and related to the Rous sarcoma virus transforming protein},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61946},
year = {1982},
abstract = {No abstract available},
subject = {Physiologische Chemie},
language = {en}
}
@article{KreftHughes1982,
author = {Kreft, J{\"u}rgen and Hughes, Colin},
title = {Cloning vectors derived from plasmids and phage of Bacillus},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-47014},
year = {1982},
abstract = {No abstract available},
language = {en}
}
@article{Scheer1982,
author = {Scheer, Ulrich},
title = {A novel type of chromatin organization in lampbrush chromosomes of Pleurodeles waltlii: visualization of clusters of tandemly repeated, very short transcriptional units},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-41087},
year = {1982},
abstract = {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.},
language = {en}
}
@article{SommervilleScheer1982,
author = {Sommerville, John and Scheer, Ulrich},
title = {Transcription of complementary repeat sequences in amphibian oocytes},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-33915},
year = {1982},
abstract = {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.},
language = {en}
}
@article{ScheerSommerville1982,
author = {Scheer, Ulrich and Sommerville, John},
title = {Sizes of chromosome loops and hnRNA molecules in oocytes of amphibia of different genome sizes},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-33094},
year = {1982},
abstract = {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.},
language = {en}
}
@article{MorenoDiazdelaEspinaFrankeKrohneetal.1982,
author = {Moreno-Diaz de la Espina, Susana and Franke, Werner W. and Krohne, Georg and Trendelenburg, Michael F. and Grund, Christine and Scheer, Ulrich},
title = {Medusoid fibril bodies: a novel type of nuclear filament of diameter 8 to 12 nm with periodic ultrastructure demonstrated in oocytes of Xenopus laevis},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-34116},
year = {1982},
abstract = {No abstract available},
language = {en}
}
@article{SchartlSchartlAnders1982,
author = {Schartl, A. and Schartl, Manfred and Anders, F.},
title = {Promotion and regression of neoplasia by testosterone-promoted cell differentiation in Xiphophorus and Girardinus},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-86684},
year = {1982},
abstract = {No abstract available.},
subject = {Schwertk{\"a}rpfling},
language = {en}
}
@article{SchartlBarnekow1982,
author = {Schartl, Manfred and Barnekow, Angelika},
title = {The expression in eukaryotes of a tyrosine kinase which is reactive with pp60v-src antibodies},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-86208},
year = {1982},
abstract = {All specimens of Eumetazoa and Parazoa, ranging from mammals, birds, teleosts, sharks, lampreys, amphioxus, insects, down to sponges showed the pp60c-src associated kinase activity, indicating that c-src, which is the cellular homologue of the oncogene v-src of Rous sarcoma virus (RSV) is probably present in all multicellular animals. Protozoa and plants did not show pp60c-src: kinase activity. The degree of c-src expression depends on the taxonomic rank of the Eumetazoa tested, and is organ-specific with nervaus tissues displaying the highest kinase activities. In the central nervous system of mammals and birds we found a high c-src expression, and in that of the lampreys, amphioxus, and insects the lowest. Unexpectedly, total extracts of sponges showed an amount of pp60c-src kinase activity similar to that of brain cell extracts of mammals and birds. These findings suggest that pp60c-src is a phylogenetic old protein that might have evolved together with the multicellular organisation of Metazoa, and that might be of importance in proliferation and differentiation of nontransformed cells.},
subject = {Protein-Tyrosin-Kinasen},
language = {en}
}
@article{HoppeFriedlSchaireretal.1983,
author = {Hoppe, J. and Friedl, P. and Schairer, H. U. and Sebald, Walter and Meyenburg, K. von and Jorgensen, B. B.},
title = {The topology of the proton translocating F\(_0\) component of the ATP synthase from E. coli K12: studies with proteases},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-62718},
year = {1983},
abstract = {The accessibility of the three F\(_0\) subunits a, b and c from the Escherichia coli Kll A TP synthase to various proteases was studied in F\(_1\)-depleted inverted membrane vesicles. Subunit b was very sensitive to all applied proteases. Chymotrypsin produced a defined fragment of mol. wt. 1S 000 which remained tightly bound to the membrane. The cleavage site was located at the C-terminal region of subunit b. Larger amounts of proteases were necessary to attack subunit a (mol. wt. 30 000). There was no detectable deavage of subunit c. It is suggested that the major hydrophilic part of subunit b extends from the membrane into the cytoplasm and is in contact with the F\(_1\) sector. The F\(_1\) sector was found to afford some protection against proteolysis oftheb subunit in vitro andin vivo. Protease digestion bad no influence on the electro-impelled H\(^+\) conduction via F\(_0\) bot ATP-dependent H\(^+\) translocation could not be reconstituted upon binding of F\(_1\)• A possible role for subunit b as a linker between catalytic events on the F\(_1\) component and the proton pathway across the membrane is discussed.},
subject = {Biochemie},
language = {en}
}
@article{KreftBurgerGoebel1983,
author = {Kreft, J{\"u}rgen and Burger, Klaus J. and Goebel, Werner},
title = {Expression of antibiotic resistance genes from Escherichia coli in Bacillus subtilis},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60600},
year = {1983},
abstract = {Bifunctional recombinant plasmids were constructed, comprised of the E. coli vectors pBR322, pBR325 and pACYC184 and different plasmids from Gram-positive bacteria, e.g. pBSU161-1 of B. subtilis and pUB110 and pC221 of S. aureus. The beta-lactamase (bla) gene and the chloramphenicol acetyltransferase (cat) gene from the E. coli plasmids were not transcribed and therefore not expressed in B. subtilis. However, tetracycline resistance from the E. coli plasmids was expressed in B. subtilis. Transcription of the tetracycline resistance gene(s) started in B. subtilis at or near the original E. coli promoter, the sequence of which is almost identical with the sequence recognized by σ55 of B. subtilis RNA polymerase.},
subject = {Biologie},
language = {en}
}
@article{KreftBergerHaertleinetal.1983,
author = {Kreft, J{\"u}rgen and Berger, Harald and H{\"a}rtlein, Michael and M{\"u}ller, Bodo and Weidinger, Gerhard and Goebel, Werner},
title = {Cloning and expression in Escherichia coli and Bacillus subtilis of the hemolysin (cereolysin) determinant from Bacillus cereus},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60596},
year = {1983},
abstract = {From a cosmid gene bank of Bacillus cereus GP4 in Escherichia coli we isolated clones which, after several days of incubation, formed hemolysis zones on erythrocyte agar plates. These clones contained recombinant cosmids with B. cereus DNA insertions of varying lengths which shared some common restriction fragments. The smallest insertionwas recloned as aPstl fragment into pJKK3-1, a shuttle vector which rep{\"u}cates in Bacillus subtilis and E. coli. When this recombinant plasmid (pJKK3-1 hly-1) was transformed into E. coli, it caused hemolysis on erythrocyte agar plates, but in liquid assays no extemal or intemal hemolytic activity could be detected with the E. coli transformants. B. subtilis carrying the same plasmid exhibited hemolytic activity at Ievels comparable to those ofthe B. cereus donor strain. The hemolysin produced in B. subtilis seemed to be indistinguishable from cereolysin in its sensitivity to cholesterol, activation by dithiothreitol, and inactivation by antibodies raised against cereolysin. When the recombinant DNA carrying the cereolysin gene was used as a probe in hybridization experiments with chromosomal DNA from a streptolysin 0-producing strain of Streptococcus pyogenes or from {\"u}steriolysin-producing strains of Usteria monoeytogenes, no positive hybridization signals were obtained. These data soggest that the genes for these three SH-activated cytolysins do not have extended sequence homology.},
subject = {Biologie},
language = {en}
}
@article{HaertleinSchiesslWagneretal.1983,
author = {H{\"a}rtlein, Michael and Schiessl, Sigrid and Wagner, Wilma and Rdest, Ursula and Kreft, J{\"u}rgen and Goebel, Werner},
title = {Transport of hemolysin by Escherichia coli},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-60619},
year = {1983},
abstract = {No abstract available},
subject = {Biologie},
language = {en}
}
@article{ScheerLanfranchiRoseetal.1983,
author = {Scheer, Ulrich and Lanfranchi, Gerolamo and Rose, Kathleen M. and Franke, Werner W. and Ringertz, Nils R.},
title = {Migration of rat RNA polymerase I into chick erythrocyte nuclei undergoing reactivation in chick-rat heterokaryons},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-33232},
year = {1983},
abstract = {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.},
language = {en}
}
@article{KleinschmidtScheerDabauvalleetal.1983,
author = {Kleinschmidt, J{\"u}rgen A. and Scheer, Ulrich and Dabauvalle, Marie-Christine and Bustin, Michael and Franke, Werner W.},
title = {High mobility group proteins of amphibian oocytes: a large storage pool of a soluble high mobility group-1-like protein and involvement in transcriptional events},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-33250},
year = {1983},
abstract = {No abstract available},
language = {en}
}
@article{ViebrockPerzSebald1983,
author = {Viebrock, A and Perz, A and Sebald, Walter},
title = {Molecular cloning of middle-abundant mRNAs from Neurospora crassa},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-82033},
year = {1983},
abstract = {no abstract available},
subject = {Neurospora crassa},
language = {en}
}
@article{GesslerBarnekow1984,
author = {Gessler, Manfred and Barnekow, Angelika},
title = {Differential expression of the cellular oncogenes c-src and c-yes in embryonal and adult chicken tissues},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59289},
year = {1984},
abstract = {The cellular onc-genes c-src and c-yes are expressed very differently during chicken embryonic development. The c-src mRNA and its translational product are detectable at high levels in brain extracts of chicken embryos and adult chickens, whereas muscle extracts show an age-dependent decrease in the amounts of c-src-specific mRNA and pp60c-src kinase activity. In contrast, the Ievels of c-yes mRNA in brain, heart, and muscle are relatively low in early embryonic stages and increase later on to values comparable to those found for liver, while in adult animals the pattern of c-yes expression is similar to that of the c-src gene. From the close correlation between the Ievels of pp60c-src, its enzymatic activity, and its corresponding mRNA at a given stage of development and in given tissues, it appears that the expression of pp60c-src is primarily controlled at the level of transcription. It is suggested that because of the different patterns of expression, the two cellular oncogenes, c-src and c-yes, play different roles in cell proliferation during early embryonic stages as weil as in ensuing differentiation processes.},
subject = {Biochemie},
language = {en}
}
@article{ArendsSebald1984,
author = {Arends, H. and Sebald, Walter},
title = {Nucleotide sequence of the cloned mRNA and gene of the ADP/ATP carrier from Neurospora crassa},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-62684},
year = {1984},
abstract = {A cDNA complementary to the mRNA of the ADPIATP carrier from Neurospora crassa was identified among ordered cDNA clones by hybridizing total polyadenylated RNA to pools of 96 cDNA recombinant plasmids and subsequent cellfree translation of hybridization-selected mRNA. Further carrier cDNAs were found by colony fdter hybridization at a frequency of 0.2-0.3\%. The gene of the carrier was cloned and isolated on a 4.6-kbp EcoRl fragment of total Neurospora DNA, and the start of the mRNA was determined by Sl nuclease mapping. From the nucleotide sequence of the cDNA and the genomic DNA, the primary structure of the gene, of the mRNA and of the ADP I ATP carrier protein could be deduced. The gene occurs in a single copy in the genome and related genes are absent. It contains two short introns, and a pyrimidine-rieb promoter region. The mRNA has a 46-bp 5 1 end and a 219-bp 3 1 end. There is an open reading frame coding for the 313 amino acid residues of the Neurospora carrier protein. The amino acid sequence is homologous in 148 positions with the established primary structure of the beef heart carrier.},
subject = {Biochemie},
language = {en}
}
@article{VeloursEsparzaHoppeetal.1984,
author = {Velours, J. and Esparza, M. and Hoppe, J. and Sebald, Walter and Guerin, B.},
title = {Amino acid sequence of a new mitochondrially synthesized proteolipid of the ATP synthase of Saccharomyces cerevisiae},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-62695},
year = {1984},
abstract = {The purification and the amino acid sequence of a proteolipid translated on ribosomes in yeast mitochondria is reported. This protein, which is a subunit of the A TP synthase, was purified by extraction with chloroform/methanol (2/1) and subsequent chromatography on phosphocellulose and reverse phase h.p.l.c. A mol. wt. of 5500 was estimated by chromatography on Bio-Gel P-30 in 8011/o fonnie acid. The complete amino acid sequence of this protein was determined by automated solid phase Edman degradation of the whole protein and of fragments obtained after cleavage with cyanogen bromide. The sequence analysis indicates a length of 48 amino acid residues. The calculated mol. wt. of 5870 corresponds to the value found by gel chromatography. This polypeptide contains three basic residues and no negatively charged side chain. The three basic residues are clustered at the C terminus. The primary structure of this protein is in full agreement with the predicted amino acid sequence of the putative polypeptide encoded by the mitochondrial aap1 gene recently discovered in Saccharomyces cerevisiae. Moreover, this protein shows 5011/o homology with the amino acid sequence of a putative polypeptide encoded by an unidentified reading frame also discovered near the mitochondrial ATPase subunit 6 genein Aspergillus nidulans.},
subject = {Biochemie},
language = {en}
}
@article{SchmidtWachterSebaldetal.1984,
author = {Schmidt, B. and Wachter, E. and Sebald, Walter and Neupert, W.},
title = {Processing peptidase of Neurospora mitochondria. Two-step cleavage of imported ATPase subunit 9},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-62674},
year = {1984},
abstract = {Subunit 9 (dicyclohexylcarbod{\"u}mide binding protein, 'proteolipid') of the mitochondrial F 1F0-ATPase is a nuclearly coded protein in Neurospora crassa. lt is synthesized on free cytoplasmic ribosomes as a larger precursor with an NH2-terminal peptide extension. The peptide extension is cleaved ofT after transport of the protein into the mitochondria. A processing activity referred to as processing peptidase that cleaves the precursor to subunit 9 and other mitochondrial proteins is described and characterized using a cell-free system. Precursor synthesized in vitro was incubated with extracts of mitochondria. Processing peptidase required Mn2 + for its activity. Localization studies suggested that it is a soluble component of the mitochondrial matrix. The precursor was cleaved in two sequential steps via an intermediate-sized polypeptide. The intermediate form in the processing of subunit 9 was also seen in vivo and upon import of the precursor into isolated mitochondria in vitro. The two dcavage sites in the precursor molecule were determined. The data indicate that: {a) the correct NH2-terminus of the mature protein was generated, (b) the NH2-terminal amino acid of the intermediate-sized polypeptide is isoleueine in position -31. The cleavage sites show similarity ofprimary structure. It is concluded that processing peptidase removes the peptide extension from the precursor to subunit 9 (and probably other precursors) after translocation of these polypeptides (or the NHrterminal part of these polypeptides) into the matrix space of mitochondria.},
subject = {Biochemie},
language = {en}
}
@article{SchartlBarnekow1984,
author = {Schartl, Manfred and Barnekow, A.},
title = {Differential expression of the cellular src gene during vertebrate development},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61893},
year = {1984},
abstract = {No abstract available},
subject = {Physiologische Chemie},
language = {en}
}
@article{SchartlBarnekow1984,
author = {Schartl, Manfred and Barnekow, A.},
title = {Cellular src gene product detected in the freshwater sponge Spongilla lacustris},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61904},
year = {1984},
abstract = {No abstract available},
subject = {Physiologische Chemie},
language = {en}
}
@article{RiehlSchartl1984,
author = {Riehl, R. and Schartl, Manfred},
title = {A Transmission Electron Microscopical and Freeze-Etch Study of Malignant-Melanoma in Fish},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61916},
year = {1984},
abstract = {No abstract available},
subject = {Physiologische Chemie},
language = {en}
}
@article{RiehlSchartlKollinger1984,
author = {Riehl, R. and Schartl, Manfred and Kollinger, G.},
title = {Comparative studies on the ultrastructure of malignant melanoma in fish and human by freeze-etching and transmission electron microscopy},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-61920},
year = {1984},
abstract = {Malignant melanomas (MM) in the fish Xiphophorus and in humans were studied both by transmission electron microscopy (TEM) and freeze-etching (FE). In both fish and human melanomas the cells show interdigitations of the,plasma membranes. The nuclei are large and lobulated and have many nuclear pores. Melanosomes are abundant and melanosome complexes ("compound melanosomes") occur regularly. Pinocytotic vesicles could be demonstrated in fish and human melanomas showing iocal differences in frequency and distribution patterns in the tumor. lntercellular junctions are lacking in MM cells from fish and humans. The FE technique showed considerable advantages in demonstrating membrane-surface peculiarities such as nuclear pores or pinocytotic vesicles. The FE replicas of fish melanomas are like those of humans. These findings may support the hypothesis that melanoma in fish and humans reflect the same biological phenomenon.},
subject = {Physiologische Chemie},
language = {en}
}
@article{ScheerSchmidtZachmannHuegleetal.1984,
author = {Scheer, Ulrich and Schmidt-Zachmann, Marion S. and H{\"u}gle, Barbara and Franke, Werner W.},
title = {Identification and localization of a novel nucleolar protein of a high molecular weight by a monoclonal antibody},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-39786},
year = {1984},
abstract = {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.},
language = {en}
}
@article{ScheerHinssenFrankeetal.1984,
author = {Scheer, Ulrich and Hinssen, Horst and Franke, Werner W. and Jockusch, Brigitte M.},
title = {Microinjection of actin-binding proteins and actin antibodies demonstrates involvement of nuclear actin in transcription of lampbrush chromosomes},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-39706},
year = {1984},
abstract = {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.},
language = {en}
}
@article{ScheerHuegleHazanetal.1984,
author = {Scheer, Ulrich and H{\"u}gle, Barbara and Hazan, Rachel and Rose, Kathleen M.},
title = {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},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-33216},
year = {1984},
abstract = {Upon incubation of cultured rat cells with the adenosine analogue 5,6-dichloro-l-\&\#946;- 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.},
language = {en}
}