Sequential changes in the macrostructure and RNA-synthesizing activity of nucleolar and extranucleolar chromatin from rat liver cells during induction of DNA synthesis

The dynamics of structural changes and RNA-polymerase activity in rat liver cell chromatin caused by drastic changes in the rates of protein synthesis was investigated. Inhibition of protein synthesis after a single injection of animals with cycloheximide (0.3 mg/100 g of body weight) increased the total condensibility of chromatin. Under these conditions, the stepwise activation of RNA-polymerases I and II correlated with decondensation of chromatin. By the 6-12th hour following cycloheximide injection, a chromatin fraction enriched with RNA-polymerase I and a RNA-polymerase II-rich fraction could be isolated from liver cell nuclei.     

Effect of vitamin E on transcription in isolated nuclei and rat liver chromatin in normal status and in E-hypovitaminosis]

The effect of alpha-tocopherol on the RNA-polymerase activity in isolated rat nuclei and chromatin from normal and E-deficient rats and the possible role of tocopherol-binding proteins in this process were studied. Some differences in the RNA-polymerase activities of the nuclei were found; however, in vitro added alpha-tocopherol had no effect on the level of the label incorporation into RNA. No effect of alpha-tocopherol on this process was observed after addition of cytosol either. Analysis of chromatins from normal and E-deficient rats revealed no differences in their RNA-polymerase activities. In vitro added alpha-tocopherol increased the RNA-polymerase activity of normal (but not of vitamin E-deficient) rats. Some differences in the RNA-polymerase activities were noted after addition to the incubation medium of the Triton X-100-solubilized nuclear fraction specifically binding alpha-tocopherol. This effect was enhanced in the presence of exogenous alpha-tocopherol. The susceptibility of chromatin from normal and E-deficient rats to DNAse I hydrolysis was also found to be different. It was concluded that vitamin E can influence the RNA-polymerase activity of the nuclei and chromatin as well as the chromatin structure and that alpha-tocopherol-binding proteins are necessary for the vitamin E effect on the RNA-polymerase activity to be manifested.     

Lipid peroxidation and the endogenous DNA polymerase activity of fractions of isolated liver chromatin in rats

Lipids which enter the composition of actively transcribed and repressed chromatin fractions are found to undergo a peroxidation. The peroxidation induction results in a depression of the endogenous DNA polymerase activity of these fractions. Tetrachloromethane increases the intensity of lipid peroxidation processes and induces a more marked depression of the DNA polymerase activity in all repressed chromatin fractions. It is assumed that selective action of tetrachloromethane on the studied indices of this chromatin fraction may be related to the differences of lipid composition of actively transcribed and repressed chromatin.     

DNA distribution in fractions differing in the strength of association with nuclear matrix during activation of DNA endonucleases in cell nuclei and treatment with nuclease S1

Influence of activation of Ca2+/Mg2(+)-dependent, Mn2(+)-dependent, Mg2(+)-dependent and acidic endogenous DNAses on distribution of DNA in fractions differing in tightness of association with the nuclear matrix has been investigated. In the intact cell nuclei all types of DNA-protein bonds were obscured by a tight bonding of DNA with the proteins of replicative complex. Activation of endogenous nuclease activities caused detachment of a significant chromatin fraction from the nuclear matrix, fraction of DNA remained attached to the replicative complex, small fraction of DNA was bound to the nuclear matrix with a less tight bond. The endogenous nucleases are supposed to make cuts mainly in distal parts of the chromatin loops and do not affect the replicative complex, where the tight DNA-matrix bond is localized. Single-strand DNA-specific S1-nuclease preferably attacks the latter site.