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Genetic analysis of DNA repair in Aspergillus: evidence for different types of MMS-sensitive hyperrec mutants
Abstract:
To identify genes which affect DNA repair and possibly recombination in Aspergillus nidulans, mutants hypersensitive to methyl methanesulphonate (MMS) were induced with ultraviolet light (UV) or gamma-rays. About half of them contained associated translocations and many were hypersensitive to UV and/or defective in meiosis. Two are alleles of the known uvsB gene while most others define new genes. In addition, among available uvs mutants many were found to be MMS-sensitive. Some of the various uncharacterized ones were identified as alleles of known uvs, but 5 of them were mapped in 2 new genes, uvsH and uvsJ. To identify functional and epistatic groups, mutants from each uvs gene were tested for effects on recombination and mutation, and double mutant uvs strains were compared for UV survival to their component single mutant strains. 3 epistatic pairs were identified, (1) uvsF and H, (2) uvsB and D, and (3) uvsC and E. Conclusive interpair tests were difficult, because such double mutant combinations were frequently lethal or nearly so. The first pair, uvsF and H, shared some of the properties of excision-defective mutants, both uvs being very highly sensitive to UV for mutation as well as survival. But unlike such mutants, uvsH was also sensitive to gamma-rays and defective in meiosis. Both uvs showed normal levels of meiotic recombination, but greatly increased spontaneous mitotic crossing-over, being the most "hyperrec" types among all uvs. The second pair, uvsB and uvsC, which was similarly hyperrec showed only slight increases of UV-induced mutation (less than 2-fold). As a main effect, these uvs caused very high frequencies of unbalanced, unstable segregants from diploid conidia (30 X), but few of these were recognizable aneuploids. The third pair, uvsC and E, which are known to be rec- for gene conversion, caused reduced mitotic crossing-over in diploids and increased levels of haploid segregants. These mutants are spontaneous mutators, but showed less UV-induced mutation than wild-type controls.
Insights
Researchers identified new genes in Aspergillus nidulans affecting DNA repair and recombination. Mutants sensitive to methyl methanesulphonate (MMS) revealed genes involved in DNA repair, recombination, and meiosis.
Area of Science:
- * Genetics
- * Molecular Biology
- * Mycology
Background:
- * DNA repair and recombination are crucial for genomic stability.
- * Understanding these processes in model organisms like Aspergillus nidulans provides fundamental insights.
- * Methyl methanesulfonate (MMS) and ultraviolet (UV) light are common mutagens used to study DNA repair pathways.
Purpose of the Study:
- * To identify novel genes in Aspergillus nidulans that influence DNA repair and recombination.
- * To characterize the function and epistasis of these newly identified genes.
- * To investigate the roles of these genes in sensitivity to mutagens and meiotic processes.
Main Methods:
- * Induction of mutants hypersensitive to methyl methanesulfonate (MMS) using UV or gamma-ray radiation.
- * Genetic screening and mapping of MMS-sensitive mutants to identify new genes (uvsH, uvsJ).
- * Analysis of double mutants to determine gene epistasis, effects on UV survival, recombination, mutation rates, and meiotic defects.
Main Results:
- * Identification of new genes (uvsH, uvsJ) involved in DNA repair and recombination, alongside alleles of the known uvsB gene.
- * Discovery of three epistatic gene pairs: (uvsF, uvsH), (uvsB, uvsD), and (uvsC, uvsE).
- * Characterization of distinct mutant phenotypes, including hypersensitivity to UV/gamma rays, meiotic defects, increased spontaneous mitotic crossing-over, and altered mutation rates.
Conclusions:
- * Several new genes controlling DNA repair and recombination pathways in Aspergillus nidulans have been identified and functionally characterized.
- * The study elucidates complex genetic interactions and epistasis among DNA repair genes.
- * These findings contribute to a deeper understanding of genome maintenance mechanisms and their regulation.