HSt participated in the design of the study and helped to draft the manuscript. EH participated in the sequence analysis and alignment. HS conceived of the study, participated in its design and coordination, helped to draft the manuscript, and gave final approval of the version to be published. All authors read and approved the final manuscript.”
“Background In Saccharomyces cerevisiae, defective DNA replication stimulates homologous recombination (HR), suggesting that the lesions that accumulate following replication

failure are substrates for HR [1–11]. Rad27 is a structure-specific C59 clinical trial endonuclease [12] required for completion of lagging strand synthesis [13], and has also been implicated in base excision repair [14], and double-strand break repair by non-homologous end joining [15]. Loss of Rad27 leads to accumulation of single-stranded gaps or nicks on daughter DNA strands [2, 16]. Collision of replication forks with these lesions results in fork collapse and generation of double-strand breaks (DSB) [8, 17] that can stimulate HR. Importantly, concomitant loss of Rad27 and components of the HR apparatus leads to synthetic lethality [18–20]. These observations implicate HR in repair of DSBs that accumulate in

the absence of Rad27. Failure to repair DSBs leads to chromosome loss [21] that is greatly stimulated in rad27 null mutant cells [8], suggesting that the essential role for the HR apparatus in rad27 mutants may be prevention of lethal levels of chromosome loss. RAD59 encodes a protein that augments the ability of Rad52, the central HR protein in yeast [22, 23], to anneal complementary Lepirudin DNA strands in vitro[24], Dorsomorphin nmr and both are required for viability in rad27 null mutant cells [19, 20]. RAD59 and RAD52 are also required to repair DSBs by single-strand annealing (SSA) [21, 25–28], and HR between inverted repeats by an annealing-dependent template switch at stalled replication forks [29–31]. Since RAD59 exerts much of its effect on HR with RAD52[21, 32, 33], the function of RAD59 required in the absence of RAD27 may be in collaboration with RAD52.

The purpose of the current study was to explore the function of RAD59 required for the viability of rad27 null mutant cells. We investigated how four rad59 mutations previously characterized with respect to their effects on SSA [21, 27], affected survivorship when combined with a rad27 null mutation. We found that rad59-K166A, which alters an amino acid in a conserved, putative α-helical domain [27, 34, 35], was synthetically lethal in combination with rad27. Because learn more rad59-K166A diminishes association of Rad52 with DSBs [21], this may be a function required for the viability of rad27 null mutant cells. The rad59-K174A and rad59-F180A mutations, which alter amino acids in the same α-helical domain, and have genetically similar effects on SSA [21], were not synthetically lethal with rad27, but resulted in distinct effects on growth that correlated with their degree of inhibition of HR.