A conditional lethal mutant of Escherichia coli K12 defective in the 5' leads to 3' exonuclease associated with DNA polymerase I

Proc Natl Acad Sci U S A. 1974 May;71(5):2048-51. doi: 10.1073/pnas.71.5.2048.


A mutant strain of E. coli, initially identified by an abnormally high frequency of recombination, has been found to be defective in the 5' --> 3' exonuclease associated with DNA polymerase I, but not in the polymerase activity. This defect is tolerated at 30 degrees , but is lethal at 43 degrees . Like other polymerase I mutants, the strain is unusually sensitive to methyl methanesulfonate and to ultraviolet irradiation; it is also unable to support the growth of phage lambda defective in general recombination, and shows a reduced rate of joining of 10S "Okazaki fragments." These results demonstrate that a functional DNA polymerase I is essential for normal growth and viability in E. coli K12.

MeSH terms

  • Catalysis
  • Chromosome Mapping
  • Chromosomes, Bacterial
  • Coliphages / enzymology
  • DNA Nucleotidyltransferases / metabolism*
  • Escherichia coli / enzymology*
  • Escherichia coli / growth & development
  • Exonucleases / metabolism*
  • Genes
  • Genes, Lethal*
  • Mutation*
  • Radiation Effects
  • Recombination, Genetic
  • Temperature
  • Ultraviolet Rays


  • DNA Nucleotidyltransferases
  • Exonucleases