Interaction Of Proliferating Cell Nuclear Antigen With Pms2 Is Required For Mutla Activation And Function In Mismatch Repair

Eukaryotic MutLa (mammalian MLH1-PMS2 heterodimer; MLH1-PMS1 in yeast) functions in early steps of mismatch repair as a latent endonuclease that requires a mismatch, MutSa/beta, and DNA-loaded proliferating cell nuclear antigen (PCNA) for activation. We show here that human PCNA and MutLa interact specifically but weakly in solution to form a complex of approximately 1: 1 stoichiometry that depends on PCNA interaction with the C-terminal endonuclease domain of the MutLa PMS2 subunit. Amino acid substitution mutations within a PMS2 C-terminal (721)QRLIAP motif attenuate or abolish human MutLa interaction with PCNA, as well as PCNA-dependent activation of MutLa endonuclease, PCNAand DNA-dependent activation of MutLa ATPase, and MutLa function in in vitro mismatch repair. Amino acid substitution mutations within the corresponding yeast PMS1 motif ((723)QKLIIP) reduce or abolish mismatch repair in vivo. Coupling of a weak allele within this motif ((723)AKLIIP) with an exo1. null mutation, which individually confer only weak mutator phenotypes, inactivates mismatch repair in the yeast cell.