Mechanism of DNA segregation in prokaryotes: ParM partitioning protein of plasmid R1 co-localizes with its replicon during the cell cycle

EMBO J. 1999 Jul 15;18(14):4076-84. doi: 10.1093/emboj/18.14.4076.


The parA locus of plasmid R1 encodes a prokaryotic centromere-like system that mediates genetic stabilization of plasmids by an unknown mechanism. The locus codes for two proteins, ParM and ParR, and a centromere-like DNA region (parC) to which the ParR protein binds. We showed recently that ParR mediates specific pairing of parC-containing DNA molecules in vitro. To obtain further insight into the mechanism of plasmid stabilization, we examined the intracellular localization of the components of the parA system. We found that ParM forms discrete foci that localize to specific cellular regions in a simple, yet dynamic pattern. In newborn cells, ParM foci were present close to both cell poles. Concomitant with cell growth, new foci formed at mid-cell. A point mutation that abolished the ATPase activity of ParM simultaneously prevented cellular localization and plasmid partitioning. A parA-containing plasmid localized to similar sites, i.e. close to the poles and at mid-cell, thus indicating that the plasmid co-localizes with ParM. Double labelling of single cells showed that plasmid DNA and ParM indeed co-localize. Thus, our data indicate that parA is a true partitioning system that mediates pairing of plasmids at mid-cell and subsequently moves them to the cell poles before cell division.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphatases / genetics
  • Adenosine Triphosphatases / metabolism
  • Bacterial Proteins / analysis*
  • Bacterial Proteins / genetics
  • Bacterial Proteins / physiology
  • Cell Cycle* / drug effects
  • Cell Division / drug effects
  • Cephalexin / pharmacology
  • DNA, Bacterial / genetics
  • DNA, Bacterial / metabolism
  • DNA-Binding Proteins / analysis*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism
  • Escherichia coli / cytology
  • Escherichia coli / drug effects
  • Escherichia coli / enzymology
  • Escherichia coli / genetics*
  • Genes, Bacterial / genetics
  • Genes, Bacterial / physiology
  • Microscopy, Fluorescence
  • Models, Biological
  • Mutation
  • Plasmids / analysis
  • Plasmids / genetics*
  • Recombinant Fusion Proteins / analysis
  • Recombinant Fusion Proteins / genetics
  • Replicon / genetics*
  • Repressor Proteins / analysis
  • Repressor Proteins / genetics
  • Repressor Proteins / physiology


  • Bacterial Proteins
  • DNA, Bacterial
  • DNA-Binding Proteins
  • ParR protein, bacteria
  • Recombinant Fusion Proteins
  • Repressor Proteins
  • chromosome partition proteins, bacterial
  • Adenosine Triphosphatases
  • Cephalexin