A mutation in the MSH6 subunit of the Saccharomyces cerevisiae MSH2-MSH6 complex disrupts mismatch recognition

In yeast, MSH2 interacts with MSH6 to repair base pair mismatches and singl e nucleotide insertion/deletion mismatches and with MSH3 to recognize small loop insertion/deletion mismatches. We identified a msh6 mutation (msh6-F3 37A) that when overexpressed in wild type strains conferred a defect in bot h MSH2-MSH6- and MSH2-MSH3-dependent mismatch repair pathways. Genetic anal ysis suggested that this phenotype was due to msh6-F337A sequestering MSH2 and preventing it from interacting with MSH3 and MSH6. In UV cross-linking, filter binding, and gel retardation assays, the MSH2-msh6-F337A complex di splayed a mismatch recognition defect. These observations, in conjunction w ith ATPase and dissociation rate analysis, suggested that MSH2-msh6-F337A f ormed an unproductive complex that was unable to stably bind to mismatch DN A.