Recovery after exposure to near-ultraviolet light of cells containing 5-bromodeoxyuridine.

The survival of synchronized V79 Chinese hamster cells irradiated with near-ultraviolet light after a 1-h labeling with 5-bromodeoxyuridine (BrdUrd) is highly dependent upon the cell's position in the cell cycle at the time of irradiation (Hagan, M., and M. M. Elkind. Biophys. J. 1979. 27:75-86). In this report, we show that cells irradiated in the same S phase after BrdUrd incorporation demonstrate an ability to repair sublethal damage, in contrast to the lack of an increase in survival with dose fractionation in template-labeled cells (Ben-Hur, E., and M. M. Elkind. Mutat. Res. 1972. 14:236-245). In addition, we show that pulse-labeled cells in S phase can repair potentially lethal damage expressed by caffeine. The kinetics of these recovery processes and the absence of a caffeine effect on the repair of sublethal damage indicate that these two processes are to a large degree unrelated. We conclude that in template-labeled cells inadequate time to effect prereplicational repair precludes effective contributions to cell survival from other kinds of DNa repair processes.