Modification of UV-induced mutation frequencies in Chinese hamster cells by dose fractionation, cycloheximide and caffeine treatments

Abstract

Chinese hamster (V79) cells were irradiated with a fractionated regime of ultraviolet light (UV 1 + UV 2). The fractionation of a UV dose always increased the colony-forming ability but reduced (or it did not change) the mutation frequencies. Treatment with cycloheximide between the two UV irradiations resulted in two types of effects, depending on the protocols used. Long exposures to cycloheximide (i.e., >6 h) for the entire period between UV 1 and UV 2 or partial treatment of cycloheximide (i.e., 3h) long before UV 2 always resulted in reduced colony-forming ability and enhanced or unchanged mutation frequencies. Exposure to cycloheximide for the entire period in the short fractionated regime (i.e., 4h) between UV 1 and UV 2 or partial treatment of cycloheximide just prior to UV 2 tended to give the opposite effects. Caffeine treatment before UV 2, with or without UV 1, significantly increased the mutation frequencies. These results suggest that an error-free postreplication repair system exists in Chinese hamster cells which is inhibitable by particular cycloheximide or caffeine treatments.