The G157C mutation in the Escherichia coli sliding clamp specifically affects initiation of replication

Mol Microbiol. 2011 Jan;79(2):433-46. doi: 10.1111/j.1365-2958.2010.07453.x. Epub 2010 Nov 23.


Escherichia coli cells with a point mutation in the dnaN gene causing the amino acid change Gly157 to Cys, were found to underinitiate replication and grow with a reduced origin and DNA concentration. The mutant β clamp also caused excessive conversion of ATP-DnaA to ADP-DnaA. The DnaA protein was, however, not the element limiting initiation of replication. Overproduction of DnaA protein, which in wild-type cells leads to over-replication, had no effect in the dnaN(G157C) mutant. Origins already opened by DnaA seemed to remain open for a prolonged period, with a stage of initiation involving β clamp loading, presumably limiting the initiation process. The existence of opened origins led to a moderate SOS response. Lagging strand synthesis, which also requires loading of the β clamp, was apparently unaffected. The result indicates that some aspects of β clamp activity are specific to the origin. It is possible that the origin specific activities of β contribute to regulation of initiation frequency.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism
  • Amino Acid Substitution / genetics*
  • Bacterial Proteins / metabolism
  • DNA Polymerase III / metabolism*
  • DNA Replication*
  • DNA, Bacterial / metabolism*
  • DNA-Binding Proteins / metabolism
  • Escherichia coli / genetics*
  • Mutation, Missense*


  • Bacterial Proteins
  • DNA, Bacterial
  • DNA-Binding Proteins
  • DnaA protein, Bacteria
  • Adenosine Triphosphate
  • beta subunit, DNA polymerase III
  • DNA Polymerase III