The PCNA unloader Elg1 promotes recombination at collapsed replication forks in fission yeast.

Abstract

Protein-DNA complexes can impede DNA replication and cause replication fork collapse. Whilst it is known that homologous recombination is deployed in such instances to restart replication, it is unclear how a stalled fork transitions into a collapsed fork at which recombination proteins can load. Previously we established assays in <i>Schizosaccharomyces pombe</i> for studying recombination induced by replication fork collapse at the site-specific protein-DNA barrier <i>RTS1</i> (Nguyen et al., 2015). Here, we provide evidence that efficient recruitment/retention of two key recombination proteins (Rad51 and Rad52) to <i>RTS1</i> depends on unloading of the polymerase sliding clamp PCNA from DNA by Elg1. We also show that, in the absence of Elg1, reduced recombination is partially suppressed by deleting <i>fbh1</i> or, to a lesser extent, <i>srs2</i>, which encode known anti-recombinogenic DNA helicases. These findings suggest that PCNA unloading by Elg1 is necessary to limit Fbh1 and Srs2 activity, and thereby enable recombination to proceed.