TY  - JOUR
A1  - Scheer, Ulrich
T1  - Structure of lampbrush chromosome loops during different states of transcriptional activity as visualized in the presence of physiological salt concentrations
N2  - 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.
KW  - lampbrush chromosomes
KW  - chromatin structure
KW  - electron microscopy
KW  - immunofluorescence microscopy
KW  - DNA antibodies
Y1  - 1987
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-39304
ER  - 
TY  - JOUR
A1  - Scheer, Ulrich
A1  - Messner, Karin
A1  - Hazan, Rachel
A1  - Raska, Ivan
A1  - Hansmann, Paul
A1  - Falk, Heinz
A1  - Spiess, Eberhard
A1  - Franke, Werner W.
T1  - High sensitivity immunolocalization of double and single-stranded DNA by a monoclonal antibody
N2  - A monoclonal antibody (AK 30-10) is described which specifically reacts with DNA both in double and single-stranded forms but not with other molecules and structures, including deoxyribonucleotides and RNAs. When used in immunocytochemical experiments on tissue sections and permeabilized cultured cells, this antibody detects DNA-containing structures, even when the DNA is present in very small amounts. Examples of high resolution detection include the DNA present in amplified extrachromosomal nucleoli, chromomeres of lampbrush chromosomes, mitochondria, chloroplasts and mycoplasmal particles. In immunoelectron microscopy using the immunogold technique, the DNA was localized in distinct substructures such as the "fibrillar centers" of nucleoli and certain stromal centers in chloroplasts. The antibody also reacts with DNA of chromatin of living cells, as shown by microinjection into cultured mitotic cells and into nuclei of amphibian oocytes. The potential value and the limitations of immunocytochemical DNA detection are discussed.
KW  - Cytologie
KW  - DNA antibodies
KW  - monoclonal antibodies
KW  - DNA immunolocalization
KW  - chromatin
KW  - mycoplasma tests
Y1  - 1987
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41063
ER  -