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Movement and equipositioning of plasmids by ParA filament disassembly

Simon Ringgaard1, Jeroen van Zon, Martin Howard

  • 1Centre for Bacterial Cell Biology, Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom.

Proceedings of the National Academy of Sciences of the United States of America
|November 13, 2009
PubMed

Insights

Bacterial plasmid partitioning relies on ParA protein dynamics. ParA filaments assemble between plasmids and disassemble, pulling plasmids to ensure stable inheritance and even distribution.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Cell Biology

Background:

  • Bacterial plasmids possess partitioning (par) loci for stable inheritance.
  • The par2 locus of plasmid pB171 involves ParA, ParB, and parC proteins.
  • Previous work showed ParA forming dynamic structures over the nucleoid, aiding plasmid distribution.

Purpose of the Study:

  • To elucidate the dynamic mechanism of ParA-mediated plasmid partitioning.
  • To investigate the role of ParA assembly and disassembly in plasmid movement.
  • To understand how the ParB/parC complex regulates ParA activity.

Main Methods:

  • Live-cell imaging of ParA dynamics in the presence of ParB and parC.
  • Mutational analysis of the par locus.
  • Mathematical modeling of protein and plasmid dynamics.

Main Results:

  • ParA forms dynamic cytoskeletal structures that nucleate and polymerize between plasmids.
  • Plasmids move in conjunction with disassembling ParA filaments, suggesting depolymerization-driven pulling.
  • Continuous cycles of ParA assembly and disassembly lead to regular plasmid relocation and equidistribution.
  • Mutational analysis identified the ParB/parC complex as a key regulator of ParA filament depolymerization.

Conclusions:

  • Plasmid partitioning is driven by a dynamic ParA cytoskeletal mechanism involving polymerization and depolymerization.
  • ParA filaments actively pull plasmids, ensuring their stable inheritance and even distribution within the bacterial cell.
  • The ParB/parC complex plays a crucial role in controlling ParA depolymerization, thereby regulating the partitioning process.

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