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

TitleDifferential suppression of priA2::kan phenotypes in Escherichia coli K-12 by mutations in priA, lexA, and dnaC.
Publication TypeJournal Article
Year of Publication1996
AuthorsSandler SJ, Samra HS, Clark AJ
JournalGenetics
Volume143
Issue1
Pagination5-13
Date Published1996 May
ISSN0016-6731
KeywordsBacterial Proteins, Bacteriophage phi X 174, beta-Galactosidase, Chromosomes, Bacterial, DNA Helicases, DNA Replication, DNA-Binding Proteins, Dose-Response Relationship, Radiation, Escherichia coli, Escherichia coli Proteins, Genes, Bacterial, Genetic Markers, Mutagenesis, Phenotype, Recombination, Genetic, Replication Protein A, Repressor Proteins, Serine Endopeptidases, Suppression, Genetic, Transduction, Genetic, Ultraviolet Rays
Abstract

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.

Alternate JournalGenetics
PubMed ID8722757