Practice question

MutS functions as initial mismatch sensor in E. coli mismatch repair pathway. Homodimeric ATPase encircles DNA, conducting diffusive scanning and interrogating duplex for wobble pairing or small insertion-deletion loops that distort helix geometry. Upon encountering mismatch, MutS undergoes ATP-dependent conformational change, kinking DNA about 60 degrees and forming transient sliding clamp. This activated form recruits MutL connector protein, coordinating downstream cleavage and excision steps. Without MutS recognition, proofreading escape errors persist. Homologs MSH2-MSH6 perform analogous surveillance in eukaryotes, underscoring conserved mismatch detection strategy across domains.