Lon-dependent proteolysis of CcdA is the key control for activation of CcdB in plasmid-free segregant bacteria

Mol Microbiol. 1994 Mar;11(6):1151-7. doi: 10.1111/j.1365-2958.1994.tb00391.x.


The ccd locus contributes to the stability of plasmid F by post-segregational killing of plasmid-free bacteria. The ccdB gene product is a potent cell-killing protein and its activity is negatively regulated by the CcdA protein. In this paper, we show that the CcdA protein is unstable and that the degradation of CcdA is dependent on the Lon protease. Differences in the stability of the killer CcdB protein and its antidote CcdA are the key to post-segregational killing. Because the half-life of active CcdA protein is shorter than that of active CcdB protein, persistence of the CcdB protein leads to the death of plasmid-free bacterial segregants.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • ATP-Dependent Proteases
  • Bacterial Proteins / metabolism*
  • Bacterial Toxins / metabolism*
  • Escherichia coli / genetics*
  • Escherichia coli Proteins*
  • Heat-Shock Proteins / metabolism*
  • Plasmids / genetics*
  • Protease La*
  • Serine Endopeptidases / metabolism*


  • Bacterial Proteins
  • Bacterial Toxins
  • CcdA protein, Bacteria
  • CcdB protein, Plasmid F
  • Escherichia coli Proteins
  • Heat-Shock Proteins
  • ATP-Dependent Proteases
  • Serine Endopeptidases
  • Lon protein, E coli
  • Protease La