Component of the post-replicative DNA mismatch repair system (MMR). Heterodimerizes with MSH2 to form MutS alpha, which binds to DNA mismatches thereby initiating DNA repair. MSH6 provides substrate-binding and substrate specificity to the complex. When bound, MutS alpha bends the DNA helix and shields approximately 20 base pairs. Acts mainly to repair base-base and single insertion-deletion mismatches that occur during replication, but can also repair longer insertion-deletion loops (IDLs), although with decreasing efficiency as the size of the extrahelical loop increases. After mismatch binding, forms a ternary complex with the MutL alpha heterodimer, which is thought to be responsible for directing the downstream MMR events, including strand discrimination, excision, and resynthesis. ATP binding and hydrolysis by the MutS alpha complex is crucial for MMR. Both subunits bind ATP, but with differing affinities, and their ATPase kinetics are also very different. MSH6 binds and hydrolyzes ATP rapidly, whereas MSH2 catalyzes ATP at a substantially slower rate. Binding to a mismatched base pair suppresses MSH6-catalyzed ATP hydrolysis, but not the activity of MSH2. ATP binding to both subunits is necessary to trigger a change in MutS alpha interaction with mismatched DNA, converting MutS alpha into a sliding clamp capable of hydrolysis-independent movement along DNA, and also facilitates formation of ternary complexes containing MutS and MutL proteins and the mismatch. May also be involved in resolution of recombination intermediates. Inhibited by Cd(2+). Heterodimer consisting of MSH2-MSH6 (MutS alpha). Forms a ternary complex with MutL alpha (MLH1-PMS1). MutS alpha interacts with proliferating cell nuclear antigen (PCNA/POL30). This interaction is disrupted upon binding of MutS alpha to mismatch DNA. The PIP box serves as a PCNA(POL30)-recognition and -binding motif. Present with 5330 molecules/cell in log phase SD medium. Belongs to the DNA mismatch repair MutS family.