Noncanonical contributions of MutLγ to VDE-initiated crossovers during Saccharomyces cerevisiae meiosis

In Saccharomyces cerevisiae , the meiosis-specific axis proteins Hop1 and Red1 are present nonuniformly across the genome. In a previous study, the meiosis-specific VMAl-derived endonuclease (VDE) was used to examine Spo11-independent recombination in a recombination reporter inserted in a Hop1/Red1-enriched region ( HIS4 ) and in a Hop1/Red1-poor region ( URA3 ). VDE-initiated crossovers at HIS4 were mostly dependent on Mlh3, a component of the MutLγ meiotic recombination intermediate resolvase, while VDE-initiated crossovers at URA3 were mostly Mlh3-independent. These differences were abolished in the absence of the chromosome axis remodeler Pch2, and crossovers at both loci become partly Mlh3-dependent. To test the generality of these observations, we examined inserts at six additional loci that differed in terms of Hop1/Red1 enrichment, chromosome size, and distance from centromeres and telomeres. All six loci behaved similarly to URA3 : the vast majority of VDE-initiated crossovers were Mlh3-independent. This indicates that, counter to previous suggestions, meiotic chromosome axis protein enrichment is not a primary determinant of which recombination pathway gives rise to crossovers during VDE-initiated meiotic recombination. In pch2 Δ mutants, the fraction of VDE-induced crossovers that were Mlh3-dependent increased to levels previously observed for Spo11-initiated crossovers in pch2 Δ, indicating that Pch2-dependent processes play an important role in controlling the distribution of factors necessary for MutLγ-dependent crossovers.