Genetics. Published Articles Ahead of Print: May 15, 2006, Copyright © 2006
doi:10.1534/genetics.106.055616


A more recent version of this article appeared on July 1, 2006.


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Analysis of the proteins involved in the in vivo repair of base-base mismatches and four-base loops formed during meiotic recombination in the yeast Saccharomyces cerevisiae

1 Duke University

* To whom correspondence should be addressed. E-mail: tom.petes{at}duke.edu.

Submitted on January 11, 2006
Revised on February 5, 2006
Accepted on 2 May 2006


Abstract

DNA mismatches are generated when heteroduplexes formed during recombination involve DNA strands that are not completely complementary. We 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 DNA 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. We find evidence that a novel Mlh1p-independent complex competes with an Mlhp-dependent complex for the repair of a four-base loop; repair of the four-base loop was affected by loss of the Mlh3p, and the repair defect of the mlh1 and pms1 strains was significantly smaller than that observed in the msh2 strain. We 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.

Key Words: homologous recombination, meiosis, mismatch repair, yeast




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