Endonucleolytic function of MutLalpha in human mismatch repair

Cell. 2006 Jul 28;126(2):297-308. doi: 10.1016/j.cell.2006.05.039.


Half of hereditary nonpolyposis colon cancer kindreds harbor mutations that inactivate MutLalpha (MLH1*PMS2 heterodimer). MutLalpha is required for mismatch repair, but its function in this process is unclear. We show that human MutLalpha is a latent endonuclease that is activated in a mismatch-, MutSalpha-, RFC-, PCNA-, and ATP-dependent manner. Incision of a nicked mismatch-containing DNA heteroduplex by this four-protein system is strongly biased to the nicked strand. A mismatch-containing DNA segment spanned by two strand breaks is removed by the 5'-to-3' activity of MutSalpha-activated exonuclease I. The probable endonuclease active site has been localized to a PMS2 DQHA(X)(2)E(X)(4)E motif. This motif is conserved in eukaryotic PMS2 homologs and in MutL proteins from a number of bacterial species but is lacking in MutL proteins from bacteria that rely on d(GATC) methylation for strand discrimination in mismatch repair. Therefore, the mode of excision initiation may differ in these organisms.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Base Pair Mismatch*
  • Cell Cycle Proteins / metabolism
  • Colorectal Neoplasms, Hereditary Nonpolyposis / genetics
  • DNA Repair*
  • Enzyme Activation
  • Exodeoxyribonucleases / metabolism*
  • Humans
  • Models, Genetic
  • MutS DNA Mismatch-Binding Protein / chemistry
  • MutS DNA Mismatch-Binding Protein / genetics
  • MutS DNA Mismatch-Binding Protein / metabolism*
  • Proliferating Cell Nuclear Antigen / metabolism
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Replication Protein C / metabolism
  • Saccharomyces cerevisiae Proteins / metabolism
  • Substrate Specificity


  • Cell Cycle Proteins
  • Proliferating Cell Nuclear Antigen
  • RFC1 protein, S cerevisiae
  • Recombinant Proteins
  • Saccharomyces cerevisiae Proteins
  • Adenosine Triphosphate
  • Exodeoxyribonucleases
  • exodeoxyribonuclease I
  • MutS DNA Mismatch-Binding Protein
  • Replication Protein C