THE RAD52 RECOMBINATIONAL REPAIR PATHWAY IS ESSENTIAL IN POL30 (PCNA)MUTANTS THAT ACCUMULATE SMALL SINGLE-STRANDED-DNA FRAGMENTS DURING DNA-SYNTHESIS

To identify in vivo pathways that compensate for impaired proliferatin g cell nuclear antigen (PCNA or Pol30p in yeast) activity, we performe d a synthetic lethal screen with the yeast pol30-104 mutation. We iden tified nine mutations that display synthetic lethality with po130-104; three mutations affected the structural gene for the large subunit of replication factor C (rfc1), which loads PCNA onto DNA, and six mutat ions affected three members of the R4D52 epistasis group for DNA recom binational repair (rad50, rad52, and rad57). We also found that pol30- 104 displayed synthetic lethality with mutations in other members of t he RAD52 epistasis group (rad51 and rad54), but not with mutations in members of the RAD3 nor the RAD6 epistasis group. Analysis of nine dif ferent pol30 mutations shows that the requirement for the RAD52 pathwa y is correlated with a DNA replication defect but not with the relativ e DNA repair defect caused by pol30 mutations. In addition, mutants th at require RAD52 for viability (po30-100, pol30-104, rfc1-1 and rth1 D elta) accumulate small single-stranded DNA fragments during DNA replic ation in vivo. Taken together, these data suggest that the RAD52 pathw ay is required when there are defects in the maturation of Okazaki fra gments.