[Phenomenon of pseudomutagenesis: experiments with modifiers of cell metabolism in human lymphocytes].

The term "pseudomutagens" is suggested for factors that increase the spontaneous mutation level not by induction of DNA molecule changes but as a result of inhibition of the repair of spontaneous pre-mutation lesions. The expected regularities of pseudomutagen effects, which are suitable as criteria for their identification, are considered. The experimental results on the effects of six modifiers of cell metabolism in human lymphocytes are analyzed.

[The chromosome cycle of DNA. 1971].

A hypothesis on the behaviour of DNA molecules during the cell cycle has been put forward using information on the regularities observed in the formation of chromosome aberrations while irradiating different stages of the cell cycle. The relevant statements of the hypothesis are as follows. 1) The cell cycle involves two stages of intermolecular proofs.

[Changes in radiosensitivity of chromosomes at the presynthetic stage of the mitotic cycle: role of single-stranded segments of DNA].

Formation of single-stranded DNA regions was investigated during the presynthetic stage of human lymphocyte cell cycle. Two peaks of single-stranded region production were found in about the middle and near the end of the G1 stage. Both the peaks appeared some hours earlier in gamma-irradiated cells than in control.

[Effect of free 5-bromodeoxyuridine on induction of SCE in human lymphocytes gamma-irradiated at the presynthetic stage of primary and secondary mitotic cycles].

Formation of SCE was studied in lymphocytes irradiated by 60Co gamma-rays at the G1 stage of the first or second mitotic cycles. The yield of SCEs induced by irradiation in the presence of 5-bromodeoxyuridine (BrdU) proved to be significantly higher than that obtained in the absence of BrdU. The enhancing influence of BrdU on SCE induction depends on neither replication cycle nor the molecular constitution of chromosomes under irradiation.

[The UV sensitivity of the bromodeoxyuridine-substituted chromosomes in the Chinese hamster].

Chinese hamster cells with chromosomes differently substituted for BUdR (TT-TT, TT-TB, TB-TB, TB-BB, where T is thymidine containing chromatid and B is BUdR substituted chromatid) were exposed to UV-light in phase G2 and chromosome aberrations (mainly chromatid breaks) were analysed. Breaks frequency per chromosome was proportional to BUdR content. No breaks were found in TT-TT chromosomes.