title: The specificity of UV-induced mutations at an endogenous locus in mammalian cells.
abstract: We have used a rapid in vivo recombinational method to clone and completely sequence 34 UV-induced mutants at the adenine phosphoribosyltransferase (APRT) locus of Chinese hamster ovary cells. Among the mutants recovered, 26 were single base substitutions including 17 G.C----A.T transitions and a single A.T----G.C transition. Three of the 4 possible transversions accounted for the remaining 8 mutations. The G.C----T.A transversion was not recovered. Six tandem double or closely neighboring double-base substitutions, one double mutation consisting of a G.C----T.A transversion and an adjacent frameshift, as well as one single frameshift mutation were also recovered. UV-induced mutation appears to be targeted to dipyrimidine sites with only two exceptions. These include two double mutations where only one of the base substitutions occurred at a dipyrimidine site. The observed specificity of UV-light-induced mutations at the APRT locus is consistent with the argument that G.C----A.T transitions result primarily from the (6-4) pyrimidine pyrimidone lesion. A striking resemblance in the distribution of UV-induced mutants and a collection of 30 spontaneous mutants identified recently in our laboratory was noted. Both share a common strong site of multiple occurrence and a considerable degree of overlap with respect to site specificity. We speculate therefore that DNA context plays a significant role in mutation fixation in mammalian cells.
mesh_terms: D000228:Adenine Phosphoribosyltransferase / Q000235:genetics*; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002470:Cell Survival / Q000528:radiation effects; D003001:Cloning, Molecular; D006224:Cricetinae; D004249:DNA Damage; D009154:Mutation / Q000528:radiation effects*; D010430:Pentosyltransferases / Q000235:genetics*
chemical_list: D010430:Pentosyltransferases; D000228:Adenine Phosphoribosyltransferase