Repair of base-base mismatches and four-base loops formed during meiotic recombination in S. cerevisiae

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  • March 21, 2019
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  • Stone, Jana E.
    • Affiliation: School of Medicine, Curriculum in Genetics and Molecular Biology
Abstract
  • DNA mismatches are generated when heteroduplexes formed during recombination involve DNA strands that are not completely complementary. I used tetrad analysis in Saccharomyces cerevisiae to examine the meiotic repair of a base-base mismatch and a four-base loop in a wild-type strain and in strains with mutations in genes implicated in DNA mismatch repair. Efficient repair of the base-base mismatch required Msh2p, Msh6p, Mlh1p, and Pms1p, but not Msh3p, Msh4p, Msh5p, Mlh2p, Mlh3p, Exo1p, Rad1p, Rad27p, or the proofreading exonuclease of DNA polymerase delta. Efficient repair of the four-base loop required Msh2p, Msh3p, Mlh1p, and Pms1p, but not Msh4p, Msh5p, Msh6p, Mlh2p, Mlh3p, Exo1p, Rad1p, Rad27p, or the proofreading exonuclease of DNA polymerase delta. I find evidence that a novel Mlh1p-independent complex competes with an Mlh1p-dependent complex for the repair of a four-base loop. I also found that the frequency and position of local double-strand DNA breaks affect the ratio of mismatch repair events that lead to gene conversion versus restoration of Mendelian segregation. Mutations in POL30, which encodes PCNA (proliferating cell nuclear antigen) in S. cerevisiae, increase the rate of mutations in vegetative cells. Collaborators found that mitotic recombination between homeologous sequences is slightly elevated in pol30-52 and pol30-201 strains. I showed that repair of base-base mismatches generated during meiotic recombination is decreased in both pol30 mutants; however, the repair defect associated with the hypomorphic pol30 mutants is not as severe as that observed when MSH2 is deleted. Aberrant segregation and crossovers are also decreased in the pol30 mutants. To address the role of ATP binding/hydrolysis in MMR-related processes, I examined mutations known to compromise the ATPase activity of Pms1p and Mlh1p. The results of these analyses confirm a differential requirement for the Pms1p ATPase activity in replication vs. recombination processes, while demonstrating that the Mlh1p ATPase activity is important for all examined MMR-related functions.
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  • In Copyright
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  • Petes, Thomas D.
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  • University of North Carolina at Chapel Hill
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  • Open access
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  • October 19, 2010

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