Regulation of the MLH1-MLH3 endonuclease in meiosis

Nature. 2020 Oct;586(7830):618-622. doi: 10.1038/s41586-020-2592-2. Epub 2020 Aug 19.


During prophase of the first meiotic division, cells deliberately break their DNA1. These DNA breaks are repaired by homologous recombination, which facilitates proper chromosome segregation and enables the reciprocal exchange of DNA segments between homologous chromosomes2. A pathway that depends on the MLH1-MLH3 (MutLγ) nuclease has been implicated in the biased processing of meiotic recombination intermediates into crossovers by an unknown mechanism3-7. Here we have biochemically reconstituted key elements of this pro-crossover pathway. We show that human MSH4-MSH5 (MutSγ), which supports crossing over8, binds branched recombination intermediates and associates with MutLγ, stabilizing the ensemble at joint molecule structures and adjacent double-stranded DNA. MutSγ directly stimulates DNA cleavage by the MutLγ endonuclease. MutLγ activity is further stimulated by EXO1, but only when MutSγ is present. Replication factor C (RFC) and the proliferating cell nuclear antigen (PCNA) are additional components of the nuclease ensemble, thereby triggering crossing-over. Saccharomyces cerevisiae strains in which MutLγ cannot interact with PCNA present defects in forming crossovers. Finally, the MutLγ-MutSγ-EXO1-RFC-PCNA nuclease ensemble preferentially cleaves DNA with Holliday junctions, but shows no canonical resolvase activity. Instead, it probably processes meiotic recombination intermediates by nicking double-stranded DNA adjacent to the junction points9. As DNA nicking by MutLγ depends on its co-factors, the asymmetric distribution of MutSγ and RFC-PCNA on meiotic recombination intermediates may drive biased DNA cleavage. This mode of MutLγ nuclease activation might explain crossover-specific processing of Holliday junctions or their precursors in meiotic chromosomes4.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Motifs
  • Amino Acid Sequence
  • Cell Cycle Proteins / metabolism
  • Chromosomes, Human / genetics
  • Conserved Sequence
  • Crossing Over, Genetic*
  • DNA / metabolism
  • DNA Cleavage
  • DNA Repair Enzymes / metabolism
  • DNA, Cruciform / metabolism
  • Endonucleases / metabolism*
  • Exodeoxyribonucleases / metabolism
  • Humans
  • Meiosis*
  • MutL Protein Homolog 1 / chemistry
  • MutL Protein Homolog 1 / metabolism*
  • MutL Proteins / chemistry
  • MutL Proteins / metabolism*
  • MutS Proteins / metabolism
  • Proliferating Cell Nuclear Antigen / metabolism
  • Replication Protein C / metabolism


  • Cell Cycle Proteins
  • DNA, Cruciform
  • MLH1 protein, human
  • MLH3 protein, human
  • MSH4 protein, human
  • MSH5 protein, human
  • Proliferating Cell Nuclear Antigen
  • DNA
  • EXO1 protein, human
  • Endonucleases
  • Exodeoxyribonucleases
  • MutL Protein Homolog 1
  • MutL Proteins
  • MutS Proteins
  • Replication Protein C
  • DNA Repair Enzymes