PCNA molecular recognition of different PIP motifs: Role of Tyr211 phosphorylation.

The coordination of enzymes and regulatory proteins for eukaryotic DNA replication and repair is largely achieved by Proliferating Cell Nuclear Antigen (PCNA), a toroidal homotrimeric protein that embraces the DNA duplex. Many proteins bind PCNA through a conserved sequence known as the PCNA interacting protein motif (PIP). PCNA is further regulated by different post-translational modifications. Phosphorylation at residue Y211 facilitates unlocking stalled replication forks to bypass DNA damage repair processes but increasing nucleotide misincorporation. We explore here how phosphorylation at Y211 affects PCNA recognition of the canonical PIP sequences of the regulatory proteins p21 and p15, which bind with nM and μM affinity, respectively. For that purpose, we have prepared PCNA with p-carboxymethyl-L-phenylalanine (pCMF, a mimetic of phosphorylated tyrosine) at position 211. We have also characterized PCNA binding to the non-canonical PIP sequence of the catalytic subunit of DNA polymerase δ (p125), and to the canonical PIP sequence of the enzyme ubiquitin specific peptidase 29 (USP29) which deubiquitinates PCNA. Our results show that Tyr211 phosphorylation has little effect on the molecular recognition of p21 and p15, and that the PIP sequences of p125 and USP29 bind to the same site on PCNA as other PIP sequences, but with very low affinity.