| Homologous recombination is an integral part of meiotic program and is required for proper chromosome segregation during the first meiotic division. Double Holliday junctions (dHJs) are the late recombination intermediates that in meiosis are specifically resolved to produce crossovers associated with the exchange of chromosomal arms. In Saccharomyces cerevisiae we found that there are at least six resolving pathways that promote processing of dHJs in vivo. We describe the role of Exo1 exonuclease in meiotic recombination. Specifically Exo1 catalyzes DSB resection and promotes dHJ resolution into crossovers. However, the later function of Exo1 is independent of its nuclease activity and Exo1 may promote dHJ resolution via its interaction with the putative nuclease complex Mlh1-Mlh3. In wild-type cells, the Exo1 and Mlh1-Mlh3 pathway contributes ∼50% of wild type crossovers while the rest is contributed by other joint molecule processing enzymes. We find that Sgs1, Mus81-Mms4, Yen1, Rtt107-Slx1-Slx4 and Slx1-Rad1-Rad10 complexes can also promote joint molecule resolution in vivo to produce crossovers. Finally, we present a model for dHJ resolution in wild-type cells which predicts that Exo1 together with Mlh1-Mlh3 and Mus81-Mms4 are the resolving activities responsible for the majority of meiotic, while Yen1 and Slx4-dependent pathways represent cryptic resolvases that are not involved in dHJ resolution in meiosis. |
