S. cerevisiae Srs2 helicase ensures normal recombination intermediate metabolism during meiosis and prevents accumulation of Rad51 aggregates

Laura J Hunt,Hardeep Kaur,Lydia Hulme,Jasvinder S Ahuja,Alastair S H Goldman,Emad A Ahmed,Michael Lichten,Ta-Chung Chou

doi:10.1007/s00412-019-00705-9

Abstract

We investigated the meiotic role of Srs2, a multi-functional DNA helicase/translocase that destabilises Rad51-DNA filaments and is thought to regulate strand invasion and prevent hyper-recombination during the mitotic cell cycle. We find that Srs2 activity is required for normal meiotic progression and spore viability. A significant fraction of srs2 mutant cells progress through both meiotic divisions without separating the bulk of their chromatin, although in such cells sister centromeres often separate. Undivided nuclei contain aggregates of Rad51 colocalised with the ssDNA-binding protein RPA, suggesting the presence of persistent single-strand DNA. Rad51 aggregate formation requires Spo11-induced DSBs, Rad51 strand-invasion activity and progression past the pachytene stage of meiosis, but not the DSB end-resection or the bias towards interhomologue strand invasion characteristic of normal meiosis. srs2 mutants also display altered meiotic recombination intermediate metabolism, revealed by defects in the formation of stable joint molecules. We suggest that Srs2, by limiting Rad51 accumulation on DNA, prevents the formation of aberrant recombination intermediates that otherwise would persist and interfere with normal chromosome segregation and nuclear division.

Highlights

The production of haploid gametes during meiosis requires the ordered segregation of the diploid genome, such that each chromosome is present as a single copy in daughter cells
We confirmed these phenotypes in our srs2 mutant strains, which included: srs2Δ, which produces no Srs2 protein; srs2-101, which is mutated in the predicted ATP-binding site (Rong et al 1991); and srs2-md, a replacement of the endogenous SRS2 promoter with the CLB2 promoter, where SRS2 is expressed in mitotic cells but not during meiosis (Chu et al 1998)
We propose that a major function of Srs2 during meiosis is to limit residency of Rad51 on Spo11-initiated double-strand breaks (DSBs)

Summary

Introduction

The production of haploid gametes during meiosis requires the ordered segregation of the diploid genome, such that each chromosome is present as a single copy in daughter cells. This occurs through two successive nuclear divisions (meiosis I and meiosis II) that follow a single round of DNA replication. Homologous recombination (HR) is critical during meiosis, both for the pairing and synapsis processes that bring homologues together, and for the formation of crossovers that allow their correct segregation (reviewed in Petronczki et al 2003)

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