Cell-free study of F plasmid partition provides evidence for cargo transport by a diffusion-ratchet mechanism

Proc Natl Acad Sci U S A. 2013 Apr 9;110(15):E1390-7. doi: 10.1073/pnas.1302745110. Epub 2013 Mar 11.


Increasingly diverse types of cargo are being found to be segregated and positioned by ParA-type ATPases. Several minimalistic systems described in bacteria are self-organizing and are known to affect the transport of plasmids, protein machineries, and chromosomal loci. One well-studied model is the F plasmid partition system, SopABC. In vivo, SopA ATPase forms dynamic patterns on the nucleoid in the presence of the ATPase stimulator, SopB, which binds to the sopC site on the plasmid, demarcating it as the cargo. To understand the relationship between nucleoid patterning and plasmid transport, we established a cell-free system to study plasmid partition reactions in a DNA-carpeted flowcell. We observed depletion zones of the partition ATPase on the DNA carpet surrounding partition complexes. The findings favor a diffusion-ratchet model for plasmid motion whereby partition complexes create an ATPase concentration gradient and then climb up this gradient toward higher concentrations of the ATPase. Here, we report on the dynamic properties of the Sop system on a DNA-carpet substrate, which further support the proposed diffusion-ratchet mechanism.

Publication types

  • Research Support, N.I.H., Intramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin Cytoskeleton / chemistry
  • Actins / metabolism
  • Adenosine Triphosphatases / metabolism*
  • Adenosine Triphosphate / chemistry
  • Bacteria / metabolism
  • Bacterial Proteins / metabolism*
  • Biological Transport
  • Cell-Free System / metabolism
  • Chromosomes / ultrastructure
  • DNA / chemistry
  • Diffusion
  • Escherichia coli / metabolism
  • Green Fluorescent Proteins / metabolism
  • Microfluidics
  • Microtubules / metabolism
  • Motion
  • Plasmids / metabolism*
  • Surface Properties


  • Actins
  • Bacterial Proteins
  • SopB protein, Bacteria
  • chromosome partition proteins, bacterial
  • Green Fluorescent Proteins
  • Adenosine Triphosphate
  • DNA
  • SopA protein, Bacteria
  • Adenosine Triphosphatases