A novel phenotype of an excision-repair mutant in Neurospora crassa: mutagen sensitivity of the mus-18 mutant is specific to UV.
A UV-sensitive mutant has been isolated from UV-mutagenized conidia of Neurospora crassa. The mutation responsible for the lesion was mapped in linkage group VL, proximal to the nucleolus organizer region. We designated the mutant mus-18. The sensitivity of the mus-18 mutant to UV-irradiation was not particularly high, being less than twice that of the wild-type strain. However, the frequency of mutations at the ad-3 loci induced by UV was extremely high even at low doses, under conditions where survival rates of mus-18 cells were almost identical to those of wild-type cells. Photo-reactivation of UV damage was normal in the mus-18 mutant. Sensitivity to other mutagens, such as gamma rays, 4-nitroquinoline-1-oxide, N-methyl-N'-nitro-N-nitrosoguanidine, mitomycin C and methyl methanesulfonate, was similar to that of the wild type. Fertility of the mus-18 mutant was normal in homozygous crosses. These results suggest that mus-18 is an excision-repair mutant. Measurement of endonuclease-sensitive sites (ESS) after liquid-holding recovery from UV damage revealed that ESS remained unrepaired for longer than 18 h in the mus-18 mutant, while most were eliminated within 6 h in wild-type cells and in other UV-sensitive mutants. This result suggests that mus-18 is defective in the incision step of dimer excision. The mus-18 mutant provides the first example of an excision-defective mutation in eukaryotes, which is specific to UV damage.
Ishii
C
C
Department of Regulation Biology, Faculty of Science, Saitama University, Urawa, Japan.
Nakamura
K
K
Inoue
H
H
D015112:4-Nitroquinoline-1-oxide / Q000494:pharmacology; D000477:Alkylating Agents / Q000494:pharmacology; D002874:Chromosome Mapping; D004249:DNA Damage; D004260:DNA Repair; D004269:DNA, Bacterial / Q000187:drug effects / Q000528:radiation effects*; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004587:Electrophoresis, Agar Gel; D004843:Epistasis, Genetic; D005720:Gamma Rays; D008741:Methyl Methanesulfonate / Q000494:pharmacology; D008769:Methylnitronitrosoguanidine; D016685:Mitomycin; D008937:Mitomycins / Q000494:pharmacology; D009154:Mutation; D009492:Neurospora crassa / Q000235:genetics*; D010641:Phenotype; D014466:Ultraviolet Rays
D000477:Alkylating Agents; D004269:DNA, Bacterial; D008937:Mitomycins; D008769:Methylnitronitrosoguanidine; D016685:Mitomycin; D015112:4-Nitroquinoline-1-oxide; D008741:Methyl Methanesulfonate