Delayed inhibition of subchromosomal DNA synthesis in V-79 Chinese hamster cells after gamma irradiation

Existence of a substantial fraction of replicon initiation events refractory to the effects of X irradiation in Chinese hamster cells has been reported by several laboratories. The work reported here examined whether this apparently refractive fraction resulted from a delayed inhibition of initiation events. Data obtained from velocity sedimentation studies indicated that the extent of inhibition increased over the first hour after irradiation from 35% inhibition immediately following exposure to 3 kR to 75% inhibition of initiation 1 hr after irradiation. Analysis of subsequent recovery of initiation radiosensitivity was performed using DNA fiber autoradiograms prepared from cells incubated up to 4 hr between 2-kR exposures. The data from these experiments indicated that some recovery occurs within 1 hr of irradiation and thus separation of the inhibition and recovery processes in V-79 cells may not be feasible.