TY  - CHAP
A1  - Scheer, Ulrich
A1  - Rose, Kathleen M.
T1  - Localization of RNA polymerase I in interphase cells and mitotic chromosomes by light and electron microscopic immunocytochemistry
N2  - 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.
KW  - nucleolus
KW  - nucleolus organizer
KW  - fibrillar centers
KW  - rRNA genes
KW  - anti-RNA polymerase I antibodies
Y1  - 1984
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33223
ER  - 
TY  - CHAP
A1  - Trendelenburg, Michael F.
A1  - Spring, Herbert
A1  - Scheer, Ulrich
A1  - Franke, Werner W.
T1  - Morphology of nucleolar cistrons in a plant cell, Acetabularia mediterranea
N2  - 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.
KW  - ribosomal RNA genes; electron microscopy; spread preparations
Y1  - 1974
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-32213
ER  -