A Role for the Interactions between Polδ and PCNA Revealed by Analysis of pol3-01 Yeast Mutants

Several DNA polymerases participate in DNA synthesis during genome replication and DNA repair. PCNA, a homotrimeric ring, acts as a processivity factor for DNA polymerases. 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 delta (Pol delta) is mediated by PIPs (PCNA-interacting peptides), in particular the one on Pol32, a regulatory subunit of Pol delta. Here, we demonstrate that pol3-01, an exonuclease mutant of Pol delta's catalytic subunit, exhibits a weak interaction with Pol30 compared to the WT DNA polymerase. The weak interaction activates DNA bypass pathways, leading to increased mutagenesis and sister chromatid recombination. Strengthening pol3-01 ' s weak interaction with PCNA suppresses most of the phenotypes. Our results are consistent with a model in which Pol3-01 tends to detach from the chromatin, allowing an easier replacement of Pol delta by the trans-lesion synthesis polymerase Zeta (Polz), thus leading to the increased mutagenic phenotype.

Automated summary

PCNA acts as a processivity factor and a landing pad for proteins during DNA synthesis. The interaction between PCNA and Pol delta is mediated by PIPs, specifically on Pol32. The weak interaction of the exonuclease mutant pol3-01 with PCNA leads to increased mutagenesis and sister chromatid recombination.