TY - JOUR A1 - Rungger, M. A1 - Crippa, M. A1 - Trendelenburg, M. F. A1 - Scheer, Ulrich A1 - Franke, Werner W. T1 - Visualization of rDNA spacer transcription in Xenopus oocytes treated with fluorouridine N2 - 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. Y1 - 1978 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33082 ER - TY - CHAP A1 - Trendelenburg, M. F. A1 - Franke, Werner W. A1 - Spring, H. A1 - Scheer, Ulrich T1 - Ultrastructure of transcription in the nucleoli of the green algae Acetabularia major and A. mediterranea N2 - No abstract available Y1 - 1975 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33779 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Hansmann, Paul A1 - Falk, Heinz A1 - Sitte, Peter T1 - Ultrastructural localization of DNA in two Cryptomonas species by use of a monoclonal DNA-antibody N2 - 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. KW - Cytologie Y1 - 1986 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-39746 ER - TY - CHAP A1 - Scheer, Ulrich A1 - Franke, Werner W. T1 - Transcriptional complexes of nucleolar genes N2 - No abstract available Y1 - 1976 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41072 ER - TY - CHAP A1 - Scheer, Ulrich A1 - Kleinschmidt, Jürgen A. A1 - Franke, Werner W. T1 - Transcriptional and skeletal elements in nucleoli of amphibian oocytes N2 - No abstract available Y1 - 1982 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-40625 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Trendelenburg, Michael F. A1 - Franke, Werner W. T1 - Transcription of ribosomal RNA cistrons: Correlation of morphological and biochemical data N2 - 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. Y1 - 1973 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-32195 ER - TY - JOUR A1 - Sommerville, John A1 - Scheer, Ulrich T1 - Transcription of complementary repeat sequences in amphibian oocytes N2 - 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. Y1 - 1982 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33915 ER - TY - JOUR A1 - Scheer, Ulrich T1 - The ultrastructure of the nuclear envelope of amphibian oocytes: a reinvestigation. III. Actinomycin D-induced decrease in central granules within the pores. N2 - No abstract available Y1 - 1970 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-32110 ER - TY - JOUR A1 - Franke, Werner W. A1 - Scheer, Ulrich T1 - The ultrastructure of the nuclear envelope of amphibian oocytes: a reinvestigation. II. The immature oocyte and dynamic aspects N2 - No abstract available Y1 - 1970 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-32102 ER - TY - JOUR A1 - Franke, Werner W. A1 - Scheer, Ulrich T1 - The ultrastructure of the nuclear envelope of amphibian oocytes: a reinvestigation. I. The mature oocyte N2 - 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. Y1 - 1970 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-32098 ER -