[Differences in the structural organization of the G- and R-bands detectable during the differential decondensation of chromosomes].
The ultrastructure of G- and R-bands in differentially decondensed chromosomes of Chinese hamster was studied with a gradual decrease in CaCl2 concentration in the medium. The gradual reduction of CaCl2 concentration leads to the decondensation of compact G-bands into chromonemes, chromomeres and further into DNP-fibrils. In the complete local decondensation zones (R-bands), the DNP-fibril orientation is parallel to the chromosome longitudinal axis. These zones have no lateral loops or chromomeres. Thus, different chromosome regions corresponding to G- and R-bands possess different sensibility to the decondensing action. Following the complete decondensation in the calcium-free medium chromosomes can be "reconstructed" by adding Ca2+. The data obtained permit to suggest a "fastener" model of the mitotic chromosome organization in which the chromosome represents an hierarchy of discrete structures--G-bands, chromomeres, nucleomeres (superbeads) and nucleosomes. The structural integrity of these levels is supported by specific protein "fasteners".
D000818:Animals; D002122:Calcium Chloride / Q000494:pharmacology; D002478:Cells, Cultured; D002871:Chromosome Banding / Q000379:methods*; D002875:Chromosomes / Q000187:drug effects / Q000648:ultrastructure*; D006224:Cricetinae; D003412:Cricetulus; D008677:Metaphase; D008854:Microscopy, Electron
D002122:Calcium Chloride
Razlichiia v strukturnoĭ organizatsii G- i R-segmentov, vyiavliaemye v protsesse differentsial'noĭ dekondensatsii khromosom.