title: Heteroduplex repair as an intermediate step of UV mutagenesis in yeast.
abstract: We have measured UV-induced mutation frequencies in yeast in a forward, nonselective assay system by scoring white adex ade2 double auxotrophs among parental red-pigmented ade2 clones. The frequencies of sectored and pure mutant clones were determined separately. In excision-defective strains carrying the genes rad1-1, rad3-2 and rad4-4, as well as in the double mutants, rad 1-1 rad 3-2 and rad 1-1 rad 4-4, considerably more sectored than pure clones are induced in the low-dose range; in repair-competent strains, pure mutant clones substantially outnumber the sectored clones. These results can be explained on the basis of known differences in the timing of error-prone repair during the cell division cycle; that is, we assume that error-prone repair occurs primarily before replication in RAD wild-type strains but after replication in excision-deficient mutants. It has been suggested that excision deficiency has a pleiotropic effect on heteroduplex repair and nucleotide excision repair; however, the high percentage (36.6%) of half-sectored clones found in the rad1-1 strain is hard to reconcile with this hypothesis. We propose that heteroduplex repair occurs subsequent to error-prone repair in both excision-proficient and excision-deficient strains.
mesh_terms: D002999:Clone Cells / Q000378:metabolism; D004260:DNA Repair; D004271:DNA, Fungal / Q000378:metabolism / Q000528:radiation effects*; D009154:Mutation; D011740:Pyrimidine Dimers / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D014466:Ultraviolet Rays
chemical_list: D004271:DNA, Fungal; D011740:Pyrimidine Dimers