ERCC1, PMS2 double mutant Chinese hamster ovary cells, when exposed to Ultraviolet light ( a DNA damaging agent ), showed a 7, 375-fold greater mutation frequency than wild type Chinese hamster ovary cells, and a 967-fold greater mutation frequency than the cells defective in ERCC1, alone . and account for the presence of the cells doubly deficient in PMS2 and ERCC1 [ or PMS2 and ERCC4 ( XPF ) ] in field defects associated with colon cancer.
