The mutation studies of mutagen‐sensitive and dna repair mutants of chinese hamster fibroblasts

Abstract

We have previously reported the isolation and partial characterization of DNA repair and/or mutagen‐sensitive mutant Chinese hamster cell strains. Here we present the results of a detailed study of the ultraviolet light (UV)‐induced mutability of one of these strains, UV^s−7, and provide preliminary mutability data on two additional lines, UV^r−23 and UV^s−40. UV^s−7 is extremely deficient in unscheduled DNA synthesis (UDS) but only slightly more sensitive to UV than the parental line. When examined for the UV‐inducibility of mutants resistant to ouabain, 6‐thioguanine, or diphtheria toxin, UV^s−7 was found to be hyper‐mutable at all three loci as compared to the parental line. The degree of hypermutability was not the same for any two loci. UV^s−40, a highly UV‐sensitive strain, was also found to be hypermutable at the ouabain‐resistant (oua^r) locus. UV^r−23, which is UV‐resistant and more proficient at UDS than the parental line, appeared to exhibit a tendency toward hypomutability at both the ouabain(oua^r) and 6‐thioguanine‐resistant (6TG^r) loci. Further characterization of all these lines should aid in delineating mammalian mechanisms of DNA repair and mutagenesis.