[The participation of endonuclease in the formation of extrachromosomal DNA and the possible mechanisms of the occurrence of gene amplification]. / Uchastie éndonukleazy v orbazovanii ékstrakhromosomnoi DNK i vozmozhnye mekhanizmy vozniknoveniia amplifikatsii genov.

We examined the extrachromosomal DNA (exDNA, Hirt fraction) in ethidium bromide sensitive and resistant cells of line L929. The exDNA amount is greater in the latter. The amount of exDNA in L929 cells makes 0.19% of the total cellular DNA; the exDNA amounts in cells, resistant to 5 and 50 micrograms/ml ethidium bromide are 0.22 and 0.33%, resp. Using labelling by BudR, it is shown that approximately 16% exDNA in L cells constituted amplified sequences to be excreting to the culture medium. The Zn-independent endogenous nuclease is activated in the resistant cells. The treatment with cycloheximide (50 micrograms/ml) resulted in the increase in the exDNA amount and in the activation of Zn-independent endonuclease. The data obtained suggested that the activation of Zn-independent endonuclease may lead to the increase in the exDNA amount and determine presumably a high rate of cell adaptability to environmental conditions.

[The mechanisms of the realization of the effect of glucocorticoids in aging]. / Mekhanizmy realizatsii éffekta gliukokortikoidov pri starenii.

The interaction of glycocorticoids with serum transport proteins, plasma membranes and rat liver cytoplasmic receptors progressively declines during ontogenesis, reaching its minimum at 24 months of age. Glycocorticoid receptor complexes (GRCs) binding to the rat liver nuclei and their residual fractions as well as the glycocorticoid-induced initiation of RNA-synthesis also decrease with age. The GRCs are shown to be capable of association with nuclear envelope, nuclear matrix and RNA-containing nuclear fraction isolated from the rat liver. The intracellular glycocorticoid receptor recycling requires fresh synthesis of the RNA and protein.

[The evaluation of the age-related characteristics of the structural status of the plasma membrane lipid phase in rat fatty tissue by using the method of inductive-resonance energy transfer]. / Otsenka vozrastnykh osobennostei strukturnogo sostoianiia lipidnoi fazy plazmaticheskikh membran zhirovoi tkani krys s ispol'zovaniem metoda induktivno-rezonansnogo perenosa énergii.

Using the method of inductance-resonance energy transfer from tryptophanyl residues to fluorescent pyrene probe the structural state of plasmatic membranes from adipose tissue of different age rats has been studied. The structural heterogeneity of membrane lipid phase has been revealed. The differences in physical properties of annular and bilayer lipids don't depend on age. During aging the membrane lipid viscosity including lipids of near protein area decreases, the conformation of membrane protein components alters during aging as well. The data on various effectiveness of energy transfer from tryptophanyls to pyrene probe in young and aged animals with stable polypeptide composition of membrane proteins indicates that. The structure of membrane lipid phase is suggested to be the main factor affecting the conformational state and functional activity of membrane-bound proteins during aging.

[Stability of DNA-protein complexes in cell nuclei of the rat liver during aging]. / Prochnost' sviazei v DNK-belkovykh kompleksakh iader kletok pecheni krys pri starenii.

Elevation in tightness of bonds between newly synthesized DNA and nuclear matrix proteins was increased in rat liver cells in ageing as shown by means of nucleoproteidecelite chromatography. With ageing content of loosely bound non-histone proteins was decreased in chromatin, tightly bound proteins were increased, while residual proteins remained unchanged. At the same time, elevated level of lamin B and alterations in content of some other polypeptides were found in the fraction of residual proteins of chromatin in aged animals. The phenomenon observed i.e. elevation of tightly bound DNA-protein complexes, enabled to suggest that alterations in composition of chromatin residual proteins were responsible for an increase in the rate of association in DNP complexes in ageing but not the accumulation of cross-links in the complex structure components.

[Study of the age-related features of the structural state of rat liver cell chromatin using micrococcal nuclease and circular dichroism]. / Izuchenie vozrastnykh osobennostei strukturnogo sostoianiia khromatina kletok pecheni krys s pomoshch'iu mikrokokkovoi nukleazy i krugovogo dikhroizma.

The structural state of liver cell chromatin of young (6 months-old) and aged rats was evaluated, using circular dichroism and DNA hydrolysis by micrococcal nuclease. It was found that the chromatin condensation ratio in active and non-active fractions increased upon ageing. The length of the DNA nucleosomal repeat did not change upon ageing in either chromatin fraction. An elevated chromatin condensation ratio was observed in aged rats both for the unfolded nucleosome chain and the supernucleosomal structures. The mechanisms of age-related increase in the chromatin compactization ratio at different levels of organization and in dissimilarly active fractions are different. It was suggested that the age-related differences in the degree of compactization may stimulate a decrease of the transcriptional activity of liver cell nuclei upon ageing.