Differential suppression of priA2::kan phenotypes in Escherichia coli K-12 by mutations in priA, lexA, and dnaC

Genetics. 1996 May;143(1):5-13. doi: 10.1093/genetics/143.1.5.


First identified as an essential component of the phi X174 in vitro DNA replication system, PriA has ATPase, helicase, translocase, and primosome-assembly activities. priA1::kan strains of Escherichia coli are sensitive to UV irradiation, deficient in homologous recombination following transduction, and filamentous. priA2::kan strains have eightfold higher levels of uninduced SOS expression than wild type. We show that (1) priA1::kan strains have eightfold higher levels of uninduced SOS expression, (2) priA2::kan strains are UVS and Rec-, (3) lexA3 suppresses the high basal levels of SOS expression of a priA2::kan strain, and (4) plasmid-encoded priA300 (K230R), a mutant allele retaining only the primosome-assembly activity of priA+, restores both UVR and Rec+ phenotypes to a priA2::kan strain. Finally, we have isolated 17 independent UVR Rec+ revertants of priA2::kan strains that carry extragenic suppressors. All 17 map in the C-terminal half of the dnaC gene. DnaC loads the DnaB helicase onto DNA as a prelude for primosome assembly and DNA replication. We conclude that priA's primosome-assembly activity is essential for DNA repair and recombination and that the dnaC suppressor mutations allow these processes to occur in the absence of priA.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacterial Proteins / biosynthesis
  • Bacterial Proteins / genetics*
  • Bacteriophage phi X 174 / genetics
  • Chromosomes, Bacterial
  • DNA Helicases / genetics
  • DNA Replication*
  • DNA-Binding Proteins / biosynthesis
  • DNA-Binding Proteins / genetics*
  • Dose-Response Relationship, Radiation
  • Escherichia coli / genetics*
  • Escherichia coli / radiation effects
  • Escherichia coli Proteins*
  • Genes, Bacterial / radiation effects
  • Genetic Markers
  • Mutagenesis
  • Phenotype
  • Recombination, Genetic
  • Replication Protein A
  • Repressor Proteins / genetics
  • Serine Endopeptidases / biosynthesis
  • Serine Endopeptidases / genetics*
  • Suppression, Genetic*
  • Transduction, Genetic
  • Ultraviolet Rays*
  • beta-Galactosidase / biosynthesis


  • Bacterial Proteins
  • DNA-Binding Proteins
  • DnaC protein, E coli
  • Escherichia coli Proteins
  • Genetic Markers
  • LexA protein, Bacteria
  • Replication Protein A
  • Repressor Proteins
  • sulA protein, E coli
  • beta-Galactosidase
  • Serine Endopeptidases
  • DNA Helicases