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Related Experiment Videos

Functional overlap between Sgs1-Top3 and the Mms4-Mus81 endonuclease.

V Kaliraman1, J R Mullen, W M Fricke

  • 1Department of Molecular Biology and Biochemistry Center for Advanced Biotechnology and Medicine, Rutgers University, Piscataway, New Jersey 08854, USA.

Genes & Development
|October 20, 2001
PubMed
Summary
This summary is machine-generated.

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The Mms4-Mus81 endonuclease cleaves branched DNA, particularly stalled replication forks, and plays a novel role in meiotic recombination. This enzyme is crucial for cell viability when DNA repair pathways involving BLM or Sgs1 are absent.

Area of Science:

  • Molecular Biology
  • DNA Replication and Repair
  • Genetics

Background:

  • RecQ DNA helicases, including human BLM and yeast Sgs1, complex with Topoisomerase III (Top3) to restart stalled replication forks.
  • Yeast cells deficient in SGS1 or TOP3 rely on MMS4 and MUS81 for viability, suggesting a functional link.

Purpose of the Study:

  • To characterize the Mms4-Mus81 complex as a structure-specific endonuclease.
  • To investigate the role of Mms4-Mus81 in DNA repair and meiotic recombination.

Main Methods:

  • Biochemical characterization of the Mms4-Mus81 heterodimer's nuclease activity on branched DNA substrates.
  • Genetic analysis to determine the in vivo function of Mms4-Mus81, especially in the absence of Sgs1 or BLM.
  • Comparison of Mms4-Mus81 activity with related endonucleases like Rad1-Rad10.

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Main Results:

  • Mms4 and Mus81 form an active heterodimeric endonuclease that efficiently cleaves branched DNA, including replication fork structures.
  • The Mms4-Mus81 endonuclease exhibits significantly higher activity on complex branched DNA than simple Y-forms, unlike NER complexes.
  • Genetic data reveal a novel role for Mms4-Mus81 in meiotic recombination and highlight its essentiality in sgs1Δ or blmΔ backgrounds.

Conclusions:

  • Stalled replication forks are likely substrates for Mms4-Mus81 cleavage, especially when Sgs1 or BLM is absent.
  • Mms4-Mus81-mediated double-strand break repair via homologous recombination may explain elevated sister chromatid exchange in BLM-deficient cells.
  • Mms4-Mus81 functions as a critical endonuclease in DNA replication fork stability and meiotic processes.