Involved in DNA mismatch repair (MMR), correcting insertion-deletion loops (IDLs) resulting from DNA replication, DNA damage or from recombination events between non-identical sequences during meiosis. Component of the MutLbeta heterodimer, which probably forms a ternary complex with the MutSbeta heterodimer that initially recognizes the DNA mismatches. This complex is thought to be responsible for directing the downsteam MMR events, including strand discrimination, excision, and resynthesis. Plays a major role in promoting meiotic crossing-over and is involved in maintaining the genetic stability of simple sequence repeats by correction of frameshift intermediates. Heterodimer of MLH1 and MLH3, called MutLbeta, which is involved in correction of a specific subset of IDLs when associated with MutSbeta. Expressed in reproductive tissues. Expressed during prophase I of meiosis. Reduced fertility and meiotic defects: 60 per cent reduction in crossovers and delayed prophase I progression. Belongs to the DNA mismatch repair MutL/HexB family.