Mutation and repair in an ultraviolet-sensitive Chinese hamster ovary cell line

An ultraviolet (UV) light-sensitive mutant of Chinese hamster ovary cells (CHO) has been isolated and characterized with respect to a number of post-irradiation responses. The UV-sensitive mutant, termed 43-3B, was isolated by replica plating of mutagenized CHO cells, followed by a challenge with UV radiation. 43-3B has the same growth rate and chromosome number as the wild-type CHO-9. 43-3B is hypersensitive to the lethal effects of UV light (D0 of 0.3 J/m2 as compared to 3.2 J/m2 for the wild-type). A marked UV-hypermutability is observed in 43-3B as compared to the wild-type. The UV-sensitive mutant is also sensitive to killing by simulated solar light, although the D0 ratio is not as great as for germicidal UV. A much reduced ability of recover control rates of semiconservative DNA synthesis after UV irradiation was observed in the repair-deficient 43-3B cell line, suggesting that the removal of UV-induced replication blocks by excision repair is the most important factor in allowing recovery of UV-inhibited DNA synthesis. Recovery of colony-forming ability between fractionated UV exposures was observed in the wild-type CHO-9, but little recovery was seen in 43-3B. This indicates that excision repair capability can also be important in split-fluence recovery