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Mutagen sensitivities and mutator effects of MMS-sensitive mutants in Neurospora
Abstract:
7 mus (mutagen-sensitive) mutants of Neurospora crassa, which are more sensitive to the toxic effects of MMS (methyl methanesulfonate) than wild-type, were investigated for cross-sensitivities to other mutagens and inhibitors. These mutants have recently been mapped in 5 new genes, mus-7 to mus-11, and mutant alleles from each gene were checked for their effects on mutation frequencies. It was found that mutants in 3 of these 5 genes showed radiation-induced mutation frequencies similar to wild-type. These included 2 alleles of the gene mus-10, which were cross-sensitive only to UV and were the only mutants that produced some viable ascospores in homozygous crosses. The mutant of the second gene, mus-8, was especially sensitive to UV and mitomycin C and produced slightly reduced frequencies of spontaneous mutation. In contrast, the mutant of the third gene, mus-7, was not UV-sensitive but showed some cross-sensitivity to X-rays; mus-7 was highly sensitive to MMS and also to histidine, which inhibits various repair-defective mutants at concentrations well below those that reduce wild-type growth. None of these mus resemble mutants previously found in Neurospora, nor do they conform clearly to mutant types identified in E. coli or yeast. On the other hand mutants in 2 further genes, mus-11, and especially 2 alleles of mus-9, are very similar to uvs-3 of Neurospora and generally resemble mutants that are considered to be defective in "error-prone" repair. They were UV- as well as X-ray-sensitive, and showed strong spontaneous mutator effects but almost no increase in recessive lethal frequencies in heterokaryons after UV-treatments.
Insights
Seven mutagen-sensitive (mus) mutants of Neurospora crassa were analyzed for their responses to various mutagens and inhibitors. Some mutants exhibited unique sensitivities and repair characteristics, distinct from previously identified genes in this organism or other model systems.
Area of Science:
- Genetics
- Molecular Biology
- Mycology
Background:
- Seven mutagen-sensitive (mus) mutants of Neurospora crassa were identified, exhibiting increased sensitivity to methyl methanesulfonate (MMS).
- These mutants were mapped to five new genes: mus-7 to mus-11.
Purpose of the Study:
- To investigate the cross-sensitivities of these new mus mutants to various mutagens and inhibitors.
- To characterize the mutation frequencies and repair defects associated with these novel genetic loci.
Main Methods:
- Testing of seven mus mutants for cross-sensitivity to UV radiation, X-rays, mitomycin C, and histidine.
- Analysis of spontaneous and induced mutation frequencies.
- Examination of viable ascospores in homozygous crosses.
- Comparison of mutant phenotypes with known repair-defective mutants in Neurospora, E. coli, and yeast.
Main Results:
- Mutants in three genes (mus-8, mus-7, mus-10) showed distinct sensitivities; mus-10 mutants were UV-sensitive, mus-8 mutants were sensitive to UV and mitomycin C, and mus-7 mutants were sensitive to X-rays and MMS.
- Mutants in two genes (mus-11 and particularly mus-9) displayed characteristics similar to "error-prone" repair mutants, exhibiting sensitivity to both UV and X-rays, and strong spontaneous mutator effects.
- None of the investigated mus mutants closely resembled previously characterized mutants in Neurospora, E. coli, or yeast.
Conclusions:
- The five new genes (mus-7 to mus-11) represent novel genetic loci involved in DNA repair and mutagenesis in Neurospora crassa.
- Specific mutants, like mus-9 and mus-11, appear to be defective in error-prone repair pathways, while others like mus-7 and mus-8 have unique sensitivity profiles.
- These findings expand our understanding of DNA repair mechanisms and genetic variation in Neurospora.