Component of the post-replicative DNA mismatch repair system (MMR). Heterodimerizes with MSH2 to form MutS beta which binds to DNA mismatches thereby initiating DNA repair. When bound, the MutS beta heterodimer bends the DNA helix and shields approximately 20 base pairs. MutS beta recognizes large insertion-deletion loops (IDL) up to 13 nucleotides long. 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 (By similarity). Component of the DNA mismatch repair (MMR) complex composed at least of MSH2, MSH3, MSH6, PMS1 and MLH1. Heterodimer consisting of MSH2-MSH3 (MutS beta). Forms a ternary complex with MutL alpha (MLH1-PMS1). Interacts with EXO1. Interacts with MCM9. Belongs to the DNA mismatch repair MutS family. MSH3 subfamily.