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Mnd1/Hop2 facilitates Dmc1-dependent interhomolog crossover formation in meiosis of budding yeast.

ABSTRACT: During meiosis, each chromosome must pair with its homolog and undergo meiotic crossover recombination in order to segregate properly at the first meiotic division. Recombination in meiosis in Saccharomyces cerevisiae relies on two Escherichia coli recA homologs, Rad51 and Dmc1, as well as the more recently discovered heterodimer Mnd1/Hop2. Meiotic recombination in S. cerevisiae mnd1 and hop2 single mutants is initiated via double-strand breaks (DSBs) but does not progress beyond this stage; heteroduplex DNA, joint molecules, and crossovers are not detected. Whereas hop2 and mnd1 single mutants are profoundly recombination defective, we show that mnd1 rad51, hop2 rad51, and mnd1 rad17 double mutants are able to carry out crossover recombination. Interestingly, noncrossover recombination is absent, indicating a role for Mnd1/Hop2 in the designation of DSBs for noncrossover recombination. We demonstrate that in the rad51 mnd1 double mutant, recombination is more likely to occur between repetitive sequences on nonhomologous chromosomes. Our results support a model in which Mnd1/Hop2 is required for DNA-DNA interactions that help ensure Dmc1-mediated stable strand invasion between homologous chromosomes, thereby preserving genomic integrity.

SUBMITTER: Henry JM

PROVIDER: S-EPMC1446936 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Accurate chromosome segregation during meiosis relies on the presence of crossover events distributed among all chromosomes. MutS? and MutL? homologs (Msh4/5 and Mlh1/3) facilitate the formation of a prominent group of meiotic crossovers that mature within the context of an elaborate chromosomal structure called the synaptonemal complex (SC). SC proteins are required for intermediate steps in the formation of MutS?-MutL? crossovers, but whether the assembled SC structure per se is required for MutS?-MutL?-dependent crossover recombination events is unknown. Here we describe an interspecies complementation experiment that reveals that the mature SC is dispensable for the formation of Mlh3-dependent crossovers in budding yeast. Zip1 forms a major structural component of the budding yeast SC, and is also required for MutS? and MutL?-dependent crossover formation. Kluyveromyces lactis ZIP1 expressed in place of Saccharomyces cerevisiae ZIP1 in S. cerevisiae cells fails to support SC assembly (synapsis) but promotes wild-type crossover levels in those nuclei that progress to form spores. While stable, full-length SC does not assemble in S. cerevisiae cells expressing K. lactis ZIP1, aggregates of K. lactis Zip1 displayed by S. cerevisiae meiotic nuclei are decorated with SC-associated proteins, and K. lactis Zip1 promotes the SUMOylation of the SC central element protein Ecm11, suggesting that K. lactis Zip1 functionally interfaces with components of the S. cerevisiae synapsis machinery. Moreover, K. lactis Zip1-mediated crossovers rely on S. cerevisiae synapsis initiation proteins Zip3, Zip4, Spo16, as well as the Mlh3 protein, as do the crossovers mediated by S. cerevisiae Zip1. Surprisingly, however, K. lactis Zip1-mediated crossovers are largely Msh4/Msh5 (MutS?)-independent. This separation-of-function version of Zip1 thus reveals that neither assembled SC nor MutS? is required for Mlh3-dependent crossover formation per se in budding yeast. Our data suggest that features of S. cerevisiae Zip1 or of the assembled SC in S. cerevisiae normally constrain MutL? to preferentially promote resolution of MutS?-associated recombination intermediates.

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Mnd1/Hop2 facilitates Dmc1-dependent interhomolog crossover formation in meiosis of budding yeast.

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