Figure 4.

Percent survival (A) and frequencies of UV-induced 6-thioguanine resistant mutants (B) in the parent cell strain 7AGM and the hREV1 antisense RNA-expressing cell strains 7AGM-17C-R1 and 7AGM-12B-R1, plotted against fluence of 254 nm UV. The data are the average of results from four experiments with the parent strain, 7AGM; three experiments with 7AGM-17C-R1 cells; and two experiments with 7AGM-12B-R1cells. The background frequencies of mutants, which have been subtracted to obtain the frequencies induced above the background frequency by UV (23), are cited in the text. The mutant frequencies observed for untreated control and each UV fluence were corrected for the cloning efficiency of the cells determined after an 8-day expression period, i.e., at the time they were plated into selection medium containing 6-thioguanine. The average cloning efficiencies for control and UV-irradiated cells were: 7AGM cells, 33.3% ± 1.4% (SEM for four independent experiments); 7AGM-17C-R1 cells, 26.7 ± 1.3% (SEM for three independent experiments); and 7AGM-12B-R1 cells, 31.8% ± 0.9% (SEM for two independent experiments).