A dynamic polymerase exchange with Escherichia coli DNA polymerase IV replacing DNA polymerase III on the sliding clamp

J Biol Chem. 2008 Apr 25;283(17):11260-9. doi: 10.1074/jbc.M709689200. Epub 2008 Feb 28.


An assay that measures synchronized, processive DNA replication by Escherichia coli DNA polymerase III holoenzyme was used to reveal replacement of pol III by the specialized lesion bypass DNA polymerase IV when the replicative polymerase is stalled. When idled replication is restarted, a rapid burst of pol III-catalyzed synthesis accompanied by approximately 7-kb full-length products is strongly inhibited by the presence of pol IV. The production of slower-forming, shorter length DNA reflects a rapid takeover of DNA synthesis by pol IV. Here we demonstrate that pol IV rapidly (<15 s) obstructs the stable interaction between pol III* and the beta clamp (the lifetime of the complex is >5 min), causing the removal of pol III* from template DNA. We propose that the rapid replacement of pol III* on the beta clamp with pol IV is mediated by two processes, an interaction between pol IV and the beta clamp and a separate interaction between pol IV and pol III*. This newly discovered property of pol IV facilitates a dynamic exchange between the two free polymerases at the primer terminus. Our study suggests a model in which the interaction between pol III* and the beta clamp is mediated by pol IV to ensure that DNA replication proceeds with minimal interruption.

Publication types

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

MeSH terms

  • DNA / chemistry
  • DNA Polymerase III / chemistry
  • DNA Polymerase III / physiology*
  • DNA Polymerase beta / chemistry
  • DNA Polymerase beta / physiology*
  • DNA Primers / chemistry
  • DNA Replication
  • DNA, Single-Stranded / chemistry
  • Escherichia coli / enzymology
  • Gene Deletion
  • Models, Biological
  • Models, Genetic
  • Mutation
  • Nucleic Acids / chemistry
  • Protein Conformation
  • Protein Structure, Tertiary


  • DNA Primers
  • DNA, Single-Stranded
  • Nucleic Acids
  • DNA
  • DNA Polymerase III
  • DNA Polymerase beta