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Bacterial actin: architecture of the ParMRC plasmid DNA partitioning complex

Jeanne Salje1, Jan Löwe

  • 1Structural Studies, MRC Laboratory of Molecular Biology, Cambridge, UK.

The EMBO Journal
|July 25, 2008
PubMed

Insights

The R1 plasmid uses the protein ParM to segregate DNA. A protein complex, ParR-parC, acts as a clamp, stabilizing ParM filaments and driving DNA movement for accurate cell division.

Area of Science:

  • Bacterial cell division
  • Molecular mechanisms of DNA segregation
  • Prokaryotic cytoskeleton dynamics

Background:

  • The R1 plasmid utilizes ATP-driven polymerization of the actin-like protein ParM for DNA segregation.
  • Accurate segregation of low-copy number plasmids is crucial for bacterial survival.
  • ParM filaments are stabilized in vivo by binding to the centromere-like region parC via the ParR protein.

Purpose of the Study:

  • To elucidate the mechanism by which ParR-parC complexes bind and stabilize elongating ParM filaments.
  • To propose a model for the processive mechanism driving DNA segregation by ParM.
  • To understand the role of ATP hydrolysis in ParM-mediated plasmid movement.

Main Methods:

  • Biochemical assays to study protein-DNA interactions.
  • Electron microscopy to visualize ParM filament dynamics and ParR-parC complex structure.
  • In vitro reconstitution of the DNA segregation machinery.

Main Results:

  • A model where oligomeric ParR dimers bound to parC DNA form a rigid clamp.
  • This clamp stabilizes the growing end of ParM filaments, allowing monomer addition.
  • ATP hydrolysis in ParM drives a processive mechanism for ParR-parC-bound DNA movement.

Conclusions:

  • The ParR-parC complex acts as a rigid clamp that binds and stabilizes elongating ParM filaments.
  • A processive mechanism driven by ATP hydrolysis in ParM facilitates DNA segregation.
  • A single ParM filament is predicted to drive the separation of each plasmid pair.

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