title: Spontaneous mutability in UV-sensitive excision-defective strains of Saccharomyces.
abstract: The genes RAD1, RAD2, RAD3 and RAD4 encode enzymes in the pathway leading to excision repair of UV-induced DNA damage in Saccharomyces cerevisiae. Four mutant alleles of these loci (rad1-1, rad2-2, rad3-12, and rad4-3) were studied for their effect on spontaneous reversion rate to lysine and histidine independence, by means of the 1000-compartment fluctuation test of von Borstel, Cain and Steinberg. Of these four excision-defective alleles, only rad3-12 was found to substantially increase the spontaneous reversion rate of the nonsense-suppressible lys1-1 allele, both through locus reversion as well as  by forward mutation at one of eight suppressor loci. Similarly, only rad3-12 conferred a considerable increase in the reversion frequency of the missense his1-7 mutant. As the RAD3 gene product is believed to mediate the first step in the excision-repair pathway, it is assumed that spontaneous lesions in the  rad3 strain are channelled into a mutagenic repair pathway, thus accounting for  the enhanced spontaneous mutation rate.
mesh_terms: D000483:Alleles; D004260:DNA Repair; D006639:Histidine / Q000378:metabolism; D008239:Lysine / Q000378:metabolism; D009154:Mutation; D011995:Recombination, Genetic; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D006639:Histidine; D008239:Lysine