Role of Escherichia coli DNA polymerase I in conferring viability upon the dnaN159 mutant strain

J Bacteriol. 2007 Jul;189(13):4688-95. doi: 10.1128/JB.00476-07. Epub 2007 Apr 20.


The Escherichia coli dnaN159 allele encodes a mutant form of the beta-sliding clamp (beta159) that is impaired for interaction with the replicative DNA polymerase (Pol), Pol III. In addition, strains bearing the dnaN159 allele require functional Pol I for viability. We have utilized a combination of genetic and biochemical approaches to characterize the role(s) played by Pol I in the dnaN159 strain. Our findings indicate that elevated levels of Pol I partially suppress the temperature-sensitive growth phenotype of the dnaN159 strain. In addition, we demonstrate that the beta clamp stimulates the processivity of Pol I in vitro and that beta159 is impaired for this activity. The reduced ability of beta159 to stimulate Pol I in vitro correlates with our finding that single-stranded DNA (ssDNA) gap repair is impaired in the dnaN159 strain. Taken together, these results suggest that (i) the beta clamp-Pol I interaction may be important for proper Pol I function in vivo and (ii) in the absence of Pol I, ssDNA gaps may persist in the dnaN159 strain, leading to lethality of the dnaN159 DeltapolA strain.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • DNA Polymerase I / genetics
  • DNA Polymerase I / metabolism*
  • DNA Polymerase III / genetics*
  • DNA Repair
  • DNA Replication / genetics
  • DNA, Single-Stranded
  • DNA-Directed DNA Polymerase / genetics
  • DNA-Directed DNA Polymerase / metabolism
  • Escherichia coli / enzymology
  • Escherichia coli / genetics
  • Escherichia coli / radiation effects
  • Escherichia coli Proteins / genetics
  • Escherichia coli Proteins / metabolism*
  • Escherichia coli Proteins / physiology
  • Microbial Viability / genetics*
  • Microbial Viability / radiation effects
  • Mutation*
  • Sequence Analysis, DNA
  • Temperature
  • Ultraviolet Rays


  • DNA, Single-Stranded
  • Escherichia coli Proteins
  • beta subunit, DNA polymerase III
  • DNA Polymerase I
  • DNA Polymerase III
  • DNA-Directed DNA Polymerase