[Comparative characteristics of chromatin endonuclease fragments]. / Sravnitel'naia kharakteristika endonukleaznykh fragmentov khromatina.

Soluble fragments of chromatin obtained by Ca, Mg-dependent endonuclease digest of rat liver nuclei, have been separated by gel chromatography on Sepharose 4B into three zones, containing oligomers, tetramers--dimers and monomers, respectively. The content of nonhistone proteins and particularly lysine-rich histones is decreased with a transition from theoligomers to monomers. The average protein/DNA ratio of the monomers is equal to 1.36 and that of histone/DNA ratio--to 0.82. The dependence of the degree of chromatin digest by endonuclease on its protein content and conditions of isolation and incubation of nuclei is discussed. The chromatin monomer formed appears to be made up of a nucleosome and short portions of spacer DNA bound to some part of histone HI and nonhistone proteins.

[Solubilization of chromatin by an endogenous enzymic Ca2+, Mg2+-dependent factor. Activity of residual chromatin]. / Soliubilizatsiia khromatina zndogennym Ca2+, Mg2+-zavisimym faktorom. Aktivnost' trudnorastvorimogo khromatina.

An endogenous Ca2+, Mg2+-dependent factor of enzymic nature (apparently an endonuclease) digests a part of chromatin in the rat liver nuclei producing DNA fragments of an uniform size. After 60 min of incubation at 15 degrees C and pH 7.50 in the presence of 5 mM MgCl2 and 2 mM CaCl2 87-93% of the total chromatin becomes soluble. The insoluble chromatin however contains 70-85% of the in vivo newly synthesized RNA. In regenerating liver the proportion of the insoluble residual chromatin increases while the radioactivity of the newly synthesized DNA in this fraction is highest. Residual chromatin can be solubilized by ultrasonic treatment only. The Ca2+, Mg2+-dependent dissolving factor is not present either in brain or in PMN leucocyte nuclei.

[Changes in the chromatin structure of hepatocyte nuclei of rats trained to hypoxia]. / Izmeneniia struktury khromatina v iadrakh gepatotsitov krys, trenirovannykh k gipoksii

Structure of chromatin in the nuclei of the isolated surviving hepatocytes and in the isolated nuclei of hepatocytes were studied by fluorochroming with acridine orange and by microfluorimetry of fluorescenc connected with the stain chromatin at 530 and 590 nm in intact rats and in the animals trained to hypoxia in a pressure chamber for 60 days. The nuclei of hepatocytes of intact rats were distributed by fluorescence at 530 nm into three classes with the intensity ratio of 1:2:4; as to the nuclei of hepatocytes of the rats trained to hypoxia - they formed a single class corresponding to the second class of control. In intact rats the ratio of the fluorescence intensity at 590 nm to such at 530 nm (alpha coefficient) formed normal distribution; in trained rats - a bimodal distribution with a shift of the maximum in the direction of reduction and increase of alpha in comparison with control. It is supposed that in hypoxia there is a repression of one and depression of other genes in the chromatine of the nuclei of the liver.