SUMMARY: A mutant of (formerly (strain 302, mutant in ) sensitive to both the lethal effect of mitomycin C and the mutagenic effect of simple alkylating agents, but having wild-type resistance to UV light, was treated with the mutagen -methyl-'-nitro--nitrosoguanidine in an attempt to isolate strains deficient in the ability to excise UV-induced pyrimidine dimers. Three strains were isolated that were UV-sensitive, but had wild-type resistance to the lethal effect of methyl methanesulphonate and all were shown to be unable to excise pyrimidine dimers. The three strains UVS9, UVS25 and UVS78 had, in addition to the mutation in , mutations in loci designated and , respectively. When the mutant gene was replaced by its wild-type allele in all three strains they became UV- and mitomycin C-resistant. On incubating the double mutants UVS9, UVS25 and UVS78 with wild-type DNA about 50% of the transformants selected for UV resistance were mitomycin C-sensitive and about 50% resistant depending on whether the mutant or the or genes had been replaced by their wild-type alleles. Although strains mutant singly in or were UV-resistant the rates of excision of pyrimidine dimers differed between them and was slower in all of them than in the wild-type and strain 302. The results indicate that wild-type possesses two pathways for the excision of pyrimidine dimers and that mutational blocks in both must exist for the excisionless phenotype to be expressed.


Article metrics loading...

Loading full text...

Full text loading...

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error