[New method for studying the kinetics of the excision repair of DNA damages in mammalian cells].

A technique has been elaborated for analyzing the kinetics of excision repair of DNA. Previously it has been shown that inhibitors of DNA synthesis (1-beta-arabinofuranosylcytosine and hydroxyurea), taken together, drastically sensibilize human cells to the killing effects of DNA damaging agents. This sensibilization was found to depend on the ability of the cells to excision repair.

[DNA replication in HeLa cells after gamma irradiation. II. The periodicity of DNA replication in the process of giant cell formation].

HeLa G-63 cells irradiated by 5 krads of 6 degrees Co gamma-rays 1.5--2 hours after mitosis (G1-phase) were incubated in growth medium during 9 days. The number of proliferating and eliminated cells, the content of DNA per cell nucleus, and kinetics of the labeled cell fraction upon 3H-TdR continuous incubation were studied.

[DNA replication in HeLa cells after gamma irradiation. I. The period of DNA replicative synthesis after the irradiation of cells in the G1 phase with gamma rays in large doses].

HeLa G-63 cells irradiated by 5 krads of 60 Co-gamma-rays during their G1-period pass through the S-period of the same interphase just as do non-irradiated cells: the kinetics of labeled cells upon a 30 min incubation with 3H-TdR (radioautography) is the same for both irradiated and non-irradiated cell populations; the rate of 3H-thymidine incorporation during the S-period upon a 3H-TdR continuous incubation is the same for both the cell populations; the mean DNA content per nucleus of irradiated cell is doubled after the S-period (cytophotometry). With increasing the radiation dose (from 10 to 30 krads), the rate of 3H-TdR incorporation into cells falls, and the S-period is prolonged.