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Mlh1-Pms1 couples ATP-driven DNA compaction with nick-dependent endonuclease activation

Bryce W Collingwood1, Amruta N Bhalkar1, Carol M Manhart1

  • 1Department of Chemistry, Temple University, Philadelphia, PA 19122, United States.

Nucleic Acids Research
|December 3, 2025
PubMed

Insights

DNA mismatch repair uses ATP to compact DNA, aiding mismatch detection. This process shifts to a repair mode when encountering nicks, stabilizing the site for efficient DNA repair.

Area of Science:

  • Molecular Biology
  • DNA Repair Mechanisms
  • Biochemistry

Background:

  • Eukaryotic DNA mismatch repair (MMR) involves MutS homolog (MSH) and Mlh1-Pms1/PMS2 complexes.
  • Mlh1-Pms1/PMS2 nicks DNA to facilitate mismatch removal by downstream proteins.
  • The ATPase activity of Mlh1-Pms1 is essential in vivo but not for in vitro nicking, leaving its function unclear.

Purpose of the Study:

  • To elucidate the unresolved function of Mlh1-Pms1's ATPase activity in DNA mismatch repair.
  • To investigate the mechanism by which Mlh1-Pms1 interacts with DNA and other repair factors.

Main Methods:

  • Utilized yeast proteins to study Mlh1-Pms1 function in vitro.
  • Employed DNA compaction assays to observe Mlh1-Pms1 behavior on continuous DNA.
  • Conducted phased nicking assays to analyze Mlh1-Pms1 activation dynamics with replication factor C (RFC)/PCNA.

Main Results:

  • Mlh1-Pms1 uses ATP to compact continuous DNA, potentially serving as a search mechanism.
  • DNA nicking suppresses Mlh1-Pms1 compaction, leading to site stabilization.
  • The timing of Mlh1-Pms1 encountering a nick relative to RFC/PCNA dictates its activation state.

Conclusions:

  • Mlh1-Pms1 utilizes ATP-driven DNA compaction to switch between a DNA search mode and a PCNA-licensed repair mode.
  • This dynamic switching mechanism is crucial for efficient and accurate DNA mismatch repair.

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