DNA mismatch repair protein Mlh1 (MLH1)

Heterodimerizes using PMS2 to form MutL alpha, a part of this post-replicative DNA mismatch repair system (MMR). DNA repair is initiated by MutS alpha (MSH2-MSH6) or MutS beta (MSH2-MSH3) binding to a dsDNA mismatch, then MutL alpha is recruited to the heteroduplex.

Meeting of this MutL-MutS- heteroduplex ternary complex in existence of RFC and PCNA is enough to trigger endonuclease activity of PMS2. It introduces single-strand breaks close to the mismatch and thus generates new entry points for the exonuclease EXO1 to degrade the strand containing the mismatch.