PCNA Phosphorylation at Tyrosine211 Inhibits Mismatch Repair at the Initiation Step

Abstract

The proliferating cell nuclear antigen (PCNA) plays an important role in DNA replication and repair. Recent in vivo studies have shown that PCNA functions can be modulated by tyrosine211 (Tyr211) phosphorylation, leading to increase in cell proliferation and poor survival in some cancer patients. Since PCNA is required for DNA mismatch at the initiation and DNA re‐synthesis steps of DNA mismatch repair (MMR), we examined the effect of Tyr211‐phosphorylated PCNA on MMR. Tyr211‐phosphorylation and non‐phosphorylation mimic PCNAs were obtained and assayed for MMR in vitro. We demonstrate here that Tyr211‐phosphorylated PCNA blocks the in vitro MMR reaction at the initiation stage in both HeLa nuclear extract and the reconstituted MMR system, as little incision/excision product was detected in these reactions in the presence of Tyr211‐phosphorylated PCNA. However, in vitro gap‐filling and primer extension experiments suggest that the phosphorylated PCNA does not block DNA synthesis catalyzed by HeLa nuclear extract or pol δ. These observations suggest that Tyr211 phosphorylation regulates PCNA functions, possibly by promoting DNA replication but inhibiting DNA repair.