The rad59-Y92A mutation, which alters an amino acid in a separate, conserved loop domain and confers genetically check details distinct effects on SSA [27, 34] was not synthetically lethal with rad27, and had a stimulatory effect on HR. This effect was genetically equivalent to that of a null allele of SRS2, which encodes a helicase that disassembles Rad51-DNA filaments [36, 37], suggesting that Rad59 may affect association of Rad51 with replication lesions. The distinct effects of the rad59 alleles suggest that Rad59 possesses
multiple, discrete roles in responding to the consequences of dysfunctional replication. Results The rad59 mutant alleles display distinct effects on survival and growth in cells defective for lagging strand synthesis
To further explore the function of RAD59 required for viability in rad27 null mutant cells, the effects of combining the rad27::LEU2 allele with the various rad59 alleles were determined by Smad inhibitor examining their ability to yield viable spores upon co-segregation in genetic crosses. The various RAD27/rad27::LEU2 RAD59/rad59 double heterozygotes were sporulated and tetrads dissected onto rich medium (Figure 1). As observed previously, the rad27::LEU2 and rad59::LEU2 alleles did not appear together in any of the colonies arising from the spores, consistent with synthetic lethality [19, 20]. The rad59-K166A allele, which alters a conserved lysine in the region of Rad59 that corresponds to the α-helical domain of the β − β − β − α motif of human Rad52 (Additional file 1: Figure S1) [27, 34, 35] displayed the same failure to appear with the rad27::LEU2 allele, indicative of synthetic lethality. Figure 1 The rad59 mutant alleles have distinct effects
on survival in cells that are defective for lagging strand synthesis. Diploid over strains heterozygous at the RAD27 (rad27::LEU2/RAD27) and RAD59 (rad59/RAD59) loci were sporulated and tetrads dissected onto YPD medium. The resulting colonies were examined after 72 h of growth at 30°. Colonies from five representative tetrads from each strain are displayed. The genotype of each colony was determined by PCR as described in the Methods. In the inverted image, colonies possessing a rad27::LEU2 allele are boxed in black, and those possessing a rad59 allele are circled in white. The rad59-K174A and rad59-F180A alleles alter conserved amino acids in the same putative α-helical domain as rad59-K166A but were able to form viable spores upon segregation with rad27::LEU2 (Figure 1). Doubling time of the rad27::LEU2 rad59-F180A double mutant was a statistically significant (p = 0.045) 24% longer than that observed for the rad27 single mutant, which correlated with a ratio of G1 to S + G2/M cells that was a statistically significant (p = 0.0031) 2.6-fold lower (Figure 2; Additional file 1: Table S2).