[The characteristics of unscheduled DNA synthesis and of the changes in the structural parameters of human lymphocyte nuclei after the action of x-ray radiation in low doses and in combination with UV irradiation]. / Osobennosti vneplanovogo sinteza DNK i izmenenii strukturnykh parametrov iader limfotsitov cheloveka posle deistviia rentgenovskogo izlucheniia v malykh dozakh i v sochetanii s UF-oblucheniem.

Effects of X-ray low doses (0.5-25 cGy) with following UV light (254 nm, 20 J/m2) on human peripheral blood lymphocytes were studied. Reparation response registered by unscheduled DNA synthesis (UDS) activity was demonstrated to be the most intensive after action of X-rays in dose ranges 2-3 cGy and 15-20 cGy, and least intensive after 10 cGy. In those cells where UV light was followed by X-rays, dose ranges 2-3 cGy and 15-20 cGy cause essential decrease of UDS as compared with UV-light action only. The most intensive UDS was in those UV-irradiated lymphocytes which where previously exposed to 10 cGy of X-rays. At the same time 10 cGy cause minimal reparation response without UV light. Possible mechanisms of discovered phenomena are discussed. In particular, reaction on 2-3 cGy might be a reorganization of genome for adaptive response or an evolution reserve cells response. From 10 cGy the reason of reaction might be a reparation, induced by radiation.

[The effect of the environment on the repair of DNA damage in human lymphocytes]. / Vliianie okruzhaiushchei sredy na reparatsiiu povrezhdenii DNK limfotsitov cheloveka.

The dependence of UV-induced unscheduled DNA synthesis (UDS) in the unstimulated lymphocytes of human peripheral blood on the ionic strength (mu) of the culture medium has been shown. In the level of mu lower or higher than the physiological (mu ph) one, UDS significantly decreases. The effect of modification of mu due to the changes of ionic strength is absent in the lymphocytes of the classic form of xeroderma pigmentosum. The phenomenon may become useful in the development of a new test for revealing cells with a genetically or physiologically changed system of UV-induced DNA repair. The mechanisms of investigated phenomenon, particularly their dependence on the structure of chromatin, as well as the influence of ionic strength on binding of the repair enzymes with DNA are discussed.

[The dependence of DNA repair induced by genetically hazardous exposures on the ionic strength of the medium containing the cells]. / Zavisimost' reparatsii DNK, indutsirovannoi geneticheski opasnymi vozdeistviiami, ot ionnoi sily sredy, v kotoroi nakhodiatsia kletki.

The dependence of UV-induced unscheduled DNA synthesis (UDS) in non-stimulated lymphocytes of human peripheral blood on the ionic strength (mu) of the culture medium has been shown. With the level of mu lower or higher than physiological (mu ph) the UDS significantly decreases. The effect of modification of mu due to changes in ionic strength is absent in the lymphocytes of patients with the classic form of xeroderma pigmentosum. This phenomenon may become useful for development of a new test revealing cells with genetically or physiologically changed system of UV-induced DNA repair. Mechanisms of investigated phenomenon, particularly their dependence on the chromatin structure, as well as the influence of ionic strength on binding the repair enzymes with DNA are discussed.

[Attenuation of protein-nuclein interactions induced by chemical mutagens in a human fibroblast culture]. / Oslablenie belkovo-nukleinovykh vzaimodeistvii, indutsirovannoe nekotorykh khimicheskimi mutagenami v kul'ture fibroblastov cheloveka.

Using nucleoprotein celite chromatography, it has been shown that DNA of human cultured fibroblasts was strongly bound to the proteins of the nuclear matrix. N-methyl-N-nitrosourea and prospidin-active antitumor agents with marked mutagenic action--were shown to attenuate the interactions, which appeared to be partially sensitive in cultured fibroblasts from patients with Down's syndrome.

[Detection of post-repair DNA damage and heterogeneity of its distribution in fractions of metaphase chromosomes of various sizes]. / Vyiavlenie postreparatsionnykh povrezhdenii DNK i neravnomernost' ikh raspredeleniia vo fraktsiiakh metafaznykh khromosom, razlichaiushchikhsia po razmeru.

The distribution of single-strand DNA breaks induced by various N-methyl-N-nitrosourea concentrations in S-phase of the cell cycle has been studied in Djungarian hamster fibroblast culture in the isolated samples of fractions of metaphase chromosomes of varying size. For the first time, a dose-effect relationship between the molecular mass of single-stranded DNA fragments isolated in an alkaline sucrose gradient from small chromosomes and the lack of the effect on DNA in large chromosomes has been established. The phenomenon detected is being discussed in terms of structural heterogeneity of interphase nuclear chromatin, i.e. irregular distribution of eu- and heterochromatin in small and large chromosomes. Another possible explanation is the storage of various damaged chromosome fragments in small chromosomes. The data obtained, apart from their significance for chromatin structure analysis, can serve as an experimental basis for the detection of, otherwise undetectable, postreparative molecular DNA damages.

[Strengthening of the DNA-protein complex during the stationary aging of cultured cells]. / Uprochnenie DNK-belkovogo kompleksa v protsesse "statsionarnogo stareniia" kul'tiviruemykh kletok.

Accumulation of DNA-protein crosslinks during "stationary phase ageing" (i.e. with the increase of non-proliferating period) of cultured transformed Chinese hamster cells and normal embryonic diploid human fibroblasts was determined by the improved method of column chromatography using hydroxylapatite of 14C-valine, 14C-leucine and 3H-thymidine-labelled cell homogenates. Such an accumulation, however, was not observed during "stationary phase ageing" of xeroderma pigmentosum human fibroblasts. Possible mechanisms of the above phenomenon are discussed.

[Relaxation of DNA-protein interactions in mouse lymphoblastic leukemic cells exposed to antineoplastic agents]. / Oslablenie DNK-belkovykh vzaimodeistvii v kletkakh leikoznykh limfoblastov myshei pod vliianiem nekotorykh protivoopukholevykh agentov.

It has been demonstrated by nucleoproteid-celite chromatography that 1-nitroso-1-methylurea, potassium cyanate and prospidin reduce DNA-protein interactions in chromatin of cell cultures from LL mice with lymphoblastic leukemia.

[Changes in RNA synthesis induced by n-methyl-nitrosourea]. / Izmeniia v sinteze RNK, vyzyvaemye N-metil-N-nitrozomochevinoi.

N-methyl- and N-nitrosourea (NMU) methylate and carbamoylate DNA, RNA and chromatin proteins. The paper is concerned with an analysis of the MNU-induced changes in the synthesis of RNA in isolated nuclei, chromatin, and in protein-free DNA. It was found that NMU decreases the rate of the RNA synthesis in all the templates used. It was also found that a 5-10 times greater concentration is required to attain the same effect in the nuclei as in chromatin. Comparison of the effects of NMU, KNCO and KCl on the template activity of chromatin allows the conclusion that the processes of methylation rather than of carbamoylation of the template are responsible for the decreased RNA synthesis. Sedimentation of the RNA synthesized over the saccharose density gradient demonstrated that the changes in the synthesis are a consequence of the decreased molecular mass of the RNA-transcript, while the number of the RNA molecules synthesized is approximately the same in control and experiment.

[Nature of RNA synthesis on embikhin-damaged templates]. / Kharakteristika sinteza RNK na povrezhdennykh émbikhinom matritsakh.

Embichin, a bifunctional alkylating mutagenic agent, inhibits RNA-synthesizing capacity of DNA and chromatin. The template capacity for decreasing the embichin-injured chromatin is caused by substantial reduction in the number of RNA molecules synthesized by this template. When DNA extracted from embichin-injured chromatin is used as a template, its template restriction is accounted for by an approximately 5-fold decrease in the RNA average molecular weight. The deoxyribonucleoprotein complexes reconstituted from embichin-injured DNA and control chromatic proteins had a lower template capacity compared with that of DNP reconstituted from control DNA. It is concluded that both links between DNA and proteins and DNA injuries are responsible for the inhibition of genome template capacity.

[Formation of DNA--protein crosslinks and their possible elimination in cultures of normal human fibroblasts after exposure to embichin]. / Obrazovanie sshivok DNK-belok i ikh vozmozhnaia éliminatsiia v kul'ture normal'nykh fibroblastov cheloveka posle deistviia émbikhina.

New methods of radiometry and fractionation of cell lysates on hydroxyapatite were applied to determine the crosslinkage between DNA and protein induced by embiquin in cell culture of normal human skin fibroblasts. Such crosslinks were found to be formed; they were eliminated in long-term cultivation of the cells after mutagen treatment.

[Structural derangements in deoxyribonucleoprotein complex damaged by N-nitroso-N-methylurea]. / Nekotorye aspekty strukturnykh narushenii v dezoksiribonukleoproteidnom komplekse, povrezhdennom N-nitrozo-N-metilmochevinoi

The effect of deoxyribonucleoproteid (DNP) solubilization under conditions of the ionic strength of the medium approaching the physiological one depended greatly after the treatment with a mutagen - N-nitroso-N-methylurea (NMU) on the NMU concentration. Apparently, for the change of DNA into a soluble state the critical number of groups in the DNA and protein should be modified. On the basis of the data obtained by circular dichroism and viscosimetry a conclusion was drawn that after the NMU treatment the DNP complex became soluble in the solvents with the ionic strength approaching the physiological one, chiefly as the result of labilization and dissociation of DNA-protein bonds.

[Physicochemical changes in DNA and deoxyribonucleoprotein caused by potassium cyanate]. / Fiziko-khimicheskie izmeneniia v DNK i dezoksiribonukleoproteide, vyzyvaemye tsianatom kaliia

The influence of KNCO on the structural integrity of the DNP salt solutions was studied. By the methods of sedimentation, viscosimetry, spectrophotometry and circular dichroism it was shown that KNCO failed to induce degrading the polynucleotide DNA strands and weakened the bonds between the DNA and protein.