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Quantitation and Analysis of the Formation of HO-Endonuclease Stimulated Chromosomal Translocations by Single-Strand Annealing in Saccharomyces cerevisiae
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Quantitation and Analysis of the Formation of HO-Endonuclease Stimulated Chromosomal Translocations by Single-Strand Annealing in Saccharomyces cerevisiae

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Mus81-dependent double-strand DNA breaks at in vivo-generated cruciform structures in S. cerevisiae

Atina G Coté1, Susanna M Lewis

  • 1Program in Genetics and Genome Biology, Hospital for Sick Children Research Institute, 1 King's College Circle, University of Toronto, Toronto, ON M5S 1A8, Canada.

Molecular Cell
|October 17, 2008
PubMed

Insights

Long DNA palindromes form cruciform structures, leading to DNA breaks resolved by Mus81 in yeast. Unchecked palindromes cause copy number increases, highlighting their role in genome instability.

Area of Science:

  • Molecular Biology
  • Genetics
  • Genomics

Background:

  • Long DNA palindromes are associated with chromosomal rearrangements.
  • The precise molecular mechanisms, particularly cruciform resolution, remain poorly understood.
  • Holliday junction (HJ) resolvases are proposed to cleave cruciform DNA structures.

Purpose of the Study:

  • To investigate the in vivo metabolism of long DNA palindromes in eukaryotes.
  • To determine the genetic factors and molecular mechanisms involved in palindromic DNA processing.
  • To confirm the cruciform extrusion and resolution model in a eukaryotic chromatin context.

Main Methods:

  • Introduction of plasmid-borne palindromes into Saccharomyces cerevisiae.
  • Analysis of DNA break formation and resolution mechanisms.
  • Genetic analysis involving key DNA repair proteins like Mus81 and Mre11.

Main Results:

  • Site-specific DNA breaks were observed at palindromic sequences in vivo.
  • These breaks exhibited characteristics of Holliday junction resolvase activity.
  • Palindromic DNA resolution in vivo was dependent on the Mus81 endonuclease.
  • The bacterial HJ resolvase RusA could substitute for Mus81.
  • Mre11 nuclease activity was found to suppress an "escape" phenomenon, a copy number increase of episomal palindromes.

Conclusions:

  • Provides in vivo evidence for cruciform extrusion and resolution of long DNA palindromes in eukaryotic chromatin.
  • Identifies Mus81 as a key eukaryotic resolvase for cruciform structures.
  • Demonstrates a link between unchecked palindromic DNA and copy number amplification, contributing to genome instability.

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