The mut system

MutS recognizes mismatches and short insertion/deletions on hemi-methylated DNA and binds to them. MutL binds and stabilizes the complex. The MutS-MutL complex activates MutH. MutH locates a nearby methyl group and nicks the newly synthesized strand opposite the methyl group. MutU (Helicase II) unwinds the DNA from the nick in the direction of the mismatch. DNA PolI degrades and replaces the unwound DNA and DNA ligase seals the single strand break.