The mismatch repair system (MMR). A. Based on figure 3 from Bellacosa et al . Initiation of MMR by recognizing the DNA damage by the MutSα or β complex and recruiting the MutLα complex. B. Excision of the damaged strand and resynthesis in which exonuclease ExoI, proliferating cell nuclear antigen (PCNA), DNA polymerase δ or ε and DNA helicase I are suggested to play a role.