Transfer of the MSH2·MSH6 Complex from Proliferating Cell Nuclear Antigen to Mispaired Bases in DNA

Proliferating cell nuclear antigen (PCNA) is thought to play a role in DNA mismatch repair at the DNA synthesis step as well as in an earlier step. Studies showing that PCNA interacts with mispair-binding protein complexes, MSH2.MSH3 and MSH2.MSH6, and that PCNA enhances MSH2.MSH6 mispair binding specificity suggest PCNA may be involved in mispair recognition. Here we show that PCNA and MSH2.MSH6 form a stable ternary complex with a homoduplex (G/C) DNA, but MSH2.MSH6 binding to a heteroduplex (G/T) DNA disrupts MSH2.MSH6 binding to PCNA. We also found that the addition of ATP or adenosine 5'-O-(thiotriphosphate) restores MSH2.MSH6 binding to PCNA, presumably by disrupting MSH2.MSH6 binding to the heteroduplex (G/T) DNA. These results support a model in which MSH2.MSH6 binds to PCNA loaded on newly replicated DNA and is transferred from PCNA to mispaired bases in DNA.