Functional interaction of proliferating cell nuclear antigen with MSH2-MSH6 and MSH2-MSH3 complexes

Eukaryotic DNA mismatch repair requires the concerted action of several pro teins, including proliferating cell nuclear antigen (PCNA) and heterodimers of MSH2 complexed with either MSH3 or MSH6. Here we report that MSH3 and M SH6, but not MSH2, contain N-terminal sequence moths characteristic of prot eins that bind to PCNA. MSH3 and MSH6 peptides containing these motifs boun d PCNA, as did the intact Msh2-Msh6 complex. This binding was strongly redu ced when alanine was substituted for conserved residues in the moth. Yeast strains containing alanine substitutions in the PCNA binding motif of Msh6 or Msh3 had elevated mutation rates, indicating that these interactions are important for genome stability. When human MSH3 or MSH6 peptides containin g the PCNA binding motif were added to a human cell extract, mismatch repai r activity was inhibited at a step preceding DNA resynthesis. Thus, MSH3 an d MSH6 interactions with PCNA may facilitate early steps in DNA mismatch re pair and may also be important for other roles of these eukaryotic MutS hom ologs.