Changes in the mitotic cycle of Chinese hamster cells and the repair of radiation damage in cells following the action of ionizing radiation

Using DNA flow cytofluorimetry technique, the effect of ionizing and gamma irradiation on cell cycle in Chinese hamster cells of clone CHO K1 773 and of its derivative EBR-30 resistant to ethidium bromide was examined. Irradiation in doses of 1 and 5.5 Gr leads to a reduced rate of cell passing from G1 into S phase, to a prolonged S phase and to a larger postsynthetic block in EBR-30 cells than in 773 cells. Our data correlate with some delay in repair of gamma-induced (200 Gr) DNA single-strand breaks in the EBR-30 clone. Clones under investigation are not distinguished in their survival. Our results may arise from deficiency in some regulatory process usually involved in cell response to radiation-induced lesions.