[Effect of UV irradiation on the mitotic cycle of Chinese hamster cells with varying UV sensitivity. II. The temporal relations in blocked cell division].

Analysis of cell distribution through phases of the cell cycle by the method of DNA flow cytofluorimetry has been utilized to investigate effects of UV light on the first cycle after irradiation in asynchronous Chinese hamster cells with different UV-sensitivity: V79 cell line (UV resistant cells) and UV-sensitive clones CHS2 and XII. Immediately after irradiation colcemid was added to the cultures to prevent mitosis and re-entering the cell cycle. UV irradiation did not affect the rate of cell passing from G1 into S phase in UV resistant cells. In UV irradiated cultures of UV-sensitive cells, a large portion of cells was arrested in G1, the effect increasing with UV dose. Besides, a portion of cells in S phase increased and the number of cells entering the G2+M compartment was essentially reduced in UV irradiated cultures of UV-sensitive cells much more than in V79 cells. The results may point to an inhibition of replicon initiation, and a larger DNA chain elongation in UV-sensitive clones after UV irradiation.