Saccharomyces carevisiae pol30 (proliferating cell nuclear antigen) mutations impair replication fidelity and mismatch repair

To understand the role of POL30 in mutation suppression, 11 Saccharomyces c erevisiae pol30 mutator mutants were characterized. These mutants were grou ped based on their mutagenic defects. Many pol30 mutants harbor multiple mu tagenic defects and were placed in more than one group. Group A mutations ( pol30-52, -104, -108, and -126) caused defects in mismatch repair (MMR), Th ese mutants exhibited mutation rates and spectra reminiscent of MMR-defecti ve mutants and were defective in an in vivo MMR assay. The mutation rates o f group A mutants were enhanced by a msh2 or a msh6 mutation, indicating th at MMR deficiency is not the only mutagenic defect present. Group B mutants (pol30-45, -103, -105, -126, and -114) exhibited increased accumulation of either deletions alone or a combination of deletions and duplications (4 t o 60 bp). All deletion and duplication breakpoints were flanked by 3 to 7 b p of imperfect direct repeats. Genetic analysis of one representative group B mutant, pol30-126, suggested polymerase slippage as the likely mutagenic mechanism. Group C mutants (pol30-100, -103, -105, -108, and -114) accumul ated base substitutions and exhibited synergistic increases in mutation rat e when combined with msh6 mutations, suggesting increased DNA polymerase mi sincorporation as a mutagenic defect. The synthetic lethality between a gro up A mutant, pol30-104, and rad52 was almost completely suppressed by the i nactivation of MSH2. Moreover, pol30-104 caused a hyperrecombination phenot ype that was partially suppressed by a msh2 mutation. These results suggest that pol30-104 strains accumulate DNA breaks in a MSH2-dependent manner.