The Functions of Replicative DNA Polymerases in DNA Repair

Various DNA polymerases participate in DNA synthesis during genome replication and DNA repair. PCNA, a homotrimer ring composed of three identical Pol30 subunits acts as a processivity factor for DNA polymerases and thus is essential for the stability of the moving fork. PCNA also acts as a “landing pad” for proteins that interact with chromatin and DNA at the moving fork.

The interaction between PCNA and Polymerase δ (Polδ) is mediated by the PIP (PCNA-Interacting Peptide) motif in Pol32, Polδ’s subunit.

We showed that replacing the PIP motif of POL3, the catalytic subunit of Polδ, by the PIP motif of POL32 (pol3-pip32) results in cell lethality, presumably because now the polymerase is too tightly bound to PCNA. In contrast, yeast strains carrying the POL32 PIP and a mutation in the exonuclease region of POL3 (pol3-01-pip32) are viable. Interestingly, this switch of PIP suppresses the high mutation rate of pol3-01 strains. Using Y2H assay, we showed that POL3 mutants show different interaction strengths with both Pol30 and Pol32, and therefore impact the interaction of Polδ and PCNA.

We are interested in understanding the importance of the Polδ -PCNA interactions in the choice of repair pathway. These studies should add to our understanding of the basic mechanisms that maintain the genome’s integrity and aid in preventing potentially dangerous mutations.