Component of the post-replicative DNA mismatch repair system (MMR). Forms two different heterodimers: MutS alpha (msh2-msh6 heterodimer) and MutS beta (msh2-msh3 heterodimer) which binds to DNA mismatches thereby initiating DNA repair. When bound, heterodimers bend the DNA helix. MutS alpha recognizes single base mismatches and dinucleotide insertion-deletion loops (IDL) in the DNA. MutS beta recognizes larger insertion-deletion loops. After mismatch binding, MutS alpha or beta 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 play a pivotal role in mismatch repair functions. The ATPase activity associated with MutS alpha regulates binding similar to a molecular switch: mismatched DNA provokes ADP-->ATP exchange, resulting in a discernible conformational transition that converts MutS alpha into a sliding clamp capable of hydrolysis-independent diffusion along the DNA backbone. This transition is crucial for mismatch repair. MutS alpha may also play a role in DNA homologous recombination repair (By similarity). Heterodimer consisting of msh2-msh6 (MutS alpha) or msh2-msh3 (MutS beta). Both heterodimers form a ternary complex with MutL alpha (mlh1-pms1). Interacts with exo1 (By similarity). Belongs to the DNA mismatch repair MutS family.