Related Experiment Videos
Interactions among mutations affecting spontaneous mutation, mitotic recombination, and DNA repair in yeast
1Division of Biology, Kansas State University, Manhattan 66506, USA.
Abstract:
The mutant alleles mms9-1, mms13-1, or mms21-1 of Saccharomyces cerevisiae confer pleiotropic effects, including sensitivity to the alkylating agent methyl methanesulfonate, elevations in spontaneous mutation and mitotic recombination, defects in meiosis, and cross-sensitivity to radiation. We constructed double-mutant strains containing an mms mutation and a defect in either excision repair, mutagenic repair, or recombinational repair and measured the levels of spontaneous mutation and mitotic recombination. Double mutants lacking excision repair show elevations in spontaneous mutation but with predominantly unchanged levels of mitotic recombination. RAD52 function was required for the expression of the hyper-recombination phenotype of the mms9-1, mms13-1, and mms21-1 alleles; double mutants displayed the very low recombination levels characteristic of rad52 mutants. Phenotypes of double mutants containing one of the mms alleles and either of the hyper-recombination/mutator rad6-1 or rad3-102 alleles suggest that the mutagenic lesions in mms strains may not be identical to the recombinogenic lesions.
Insights
Mutations in Saccharomyces cerevisiae MMS genes cause DNA repair defects, increasing mutation rates. RAD52 is essential for the hyper-recombination phenotype associated with these MMS mutations.
Area of Science:
- Molecular Biology
- Genetics
- Yeast Genetics
Background:
- The yeast Saccharomyces cerevisiae harbors mutant alleles (mms9-1, mms13-1, mms21-1) exhibiting pleiotropic effects.
- These effects include sensitivity to methyl methanesulfonate, increased spontaneous mutation and mitotic recombination, meiotic defects, and radiation sensitivity.
Purpose of the Study:
- To investigate the roles of DNA repair pathways in the phenotypes of mms mutants.
- To construct and analyze double-mutant strains combining mms mutations with defects in excision, mutagenic, or recombinational repair.
Main Methods:
- Construction of double-mutant yeast strains.
- Measurement of spontaneous mutation and mitotic recombination levels.
- Analysis of RAD52, RAD6, and RAD3 gene functions in conjunction with mms mutations.
Main Results:
- Double mutants lacking excision repair showed increased spontaneous mutation but unchanged mitotic recombination.
- RAD52 function was critical for the hyper-recombination phenotype of mms alleles; double mutants had very low recombination levels.
- The mutagenic and recombinogenic lesions in mms strains may differ, as suggested by double mutant phenotypes with rad6-1 and rad3-102.
Conclusions:
- The mms mutations interact with different DNA repair pathways, influencing mutation and recombination rates.
- RAD52-dependent recombination is essential for the hyper-recombination phenotype observed in mms mutants.
- The study suggests distinct mechanisms underlying mutagenesis and recombination in these yeast mutants.