| Abstrakt: |
To understand the role of POL30in mutation suppression, 11 Saccharomyces cerevisiae pol30mutator mutants were characterized. These mutants were grouped based on their mutagenic defects. Many pol30mutants harbor multiple mutagenic defects and were placed in more than one group. Group A mutations (pol30-52, -104, -108, and -126) caused defects in mismatch repair (MMR). These mutants exhibited mutation rates and spectra reminiscent of MMR-defective mutants and were defective in an in vivo MMR assay. The mutation rates of group A mutants were enhanced by a msh2or a msh6mutation, indicating that 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 to 60 bp). All deletion and duplication breakpoints were flanked by 3 to 7 bp 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) accumulated base substitutions and exhibited synergistic increases in mutation rate when combined with msh6mutations, suggesting increased DNA polymerase misincorporation as a mutagenic defect. The synthetic lethality between a group A mutant, pol30-104, and rad52was almost completely suppressed by the inactivation of MSH2. Moreover, pol30-104caused a hyperrecombination phenotype that was partially suppressed by a msh2mutation. These results suggest that pol30-104strains accumulate DNA breaks in a MSH2-dependent manner. |
