Component of the post-replicative DNA mismatch repair system (MMR). Forms the heterodimer MutS beta (MSH2-MSH3 heterodimer) which binds to DNA mismatches thereby initiating DNA repair. MutS beta recognizes single base mismatches and trinucleotide insertion-deletion loops (IDL) in the DNA. Heterodimer consisting of MSH2-MSH3 (MutS beta). Belongs to the DNA mismatch repair MutS family. MSH3 subfamily.