Kinetics of DNA Repair in Ultraviolet-Irradiated and N-acetoxy-2-acetylaminofluorene-Treated Mammalian Cells.

Repair kinetics after saturating doses of ultraviolet radiation (UV), N-acetoxy-2-acetylaminofluorene (AAAF), and combinations of both agents were studied in human fibroblasts proficient and deficient in excision repair, and in Chinese hamster cells (V-79) deficient in excision repair. Three techniques were used: unscheduled DNA synthesis, photolysis of DNA repaired in the presence of bromodeoxyuridine (BrdUrd), and measurements of sites sensitive to a UV-endonuclease. The repair rate appears to be approximately constant during the first few hours after treatment. Later there is a decrease with time; the magnitude of the decrease depends on the cell line. Our data show that the decrease in repair observed in repair-deficient cells treated with combinations of both agents as compared to separate treatments is due neither to the cytotoxic effects of the agents used, nor to a shutoff of the repair system by the high concentrations of AAAF employed.