PREFERENTIAL REPAIR OF THE TRANSCRIBED DNA STRAND IN THE DIHYDROFOLATE-REDUCTASE GENE THROUGHOUT THE CELL-CYCLE IN UV-IRRADIATED HUMAN-CELLS

We examined repair of UV-induced cyclobutane pyrimidine dimers (CPD) i n each strand of the expressed dihydrofolate reductase gene in human c ells in different phases of the cell cycle: G1, early S, middle S, lat e S, and G2/M. After 4 h of incubation, repair of the transcribed stra nd was substantially more efficient than repair of the non-transcribed strand in all phases. Furthermore, we observed no remarkable cell cyc le-dependent differences in either the initial lesion frequency or the efficiency of repair of the transcribed strand. We conclude that tran scription coupled repair operates generally and with high efficiency t hroughout the cell cycle.