Refine
Has Fulltext
- yes (63)
Is part of the Bibliography
- yes (63)
Year of publication
Document Type
- Journal article (49)
- Conference Proceeding (9)
- Book article / Book chapter (4)
- Book (1)
Keywords
- Cytologie (7)
- Botanik (2)
- electron microscopy (2)
- transcription (2)
- Acetabularia (1)
- Actinomycin D (1)
- Amphibian oocytes (1)
- Anatomie (1)
- Chromatin structure (1)
- Cross-bridges (1)
- DNA antibodies (1)
- DNA immunolocalization (1)
- Deutschland (1)
- Electron microscopy (1)
- Gefäßpflanzen (1)
- Golgi apparatus (1)
- Membranes (1)
- Microtubules (1)
- Nuclear pores (1)
- Nucleocytoplasmic exchange (1)
- Nucleolus (1)
- Tetrahymena (1)
- Tumor / Zellteilung (1)
- Verzeichnis (1)
- Zelldifferenzierung (1)
- Zellkern (1)
- antibody (1)
- chromatin (1)
- evolution (1)
- gene activity (1)
- immunofluorescence (1)
- monoclonal antibodies (1)
- mycoplasma tests (1)
- nucleosomes (1)
- ribosomal RNA genes; electron microscopy; spread preparations (1)
- ribosomes (1)
- sperm (1)
Institute
- Theodor-Boveri-Institut für Biowissenschaften (63) (remove)
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.
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.
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.