title: Differential suppression of priA2::kan phenotypes in Escherichia coli K-12 by mutations in priA, lexA, and dnaC.
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.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley 94720-3202, USA. ecorec2@mendel.berkeley.edu
authors.forename: S J
authors.initials: SJ
authors.lastname: Sandler
authors.forename: H S
authors.initials: HS
authors.lastname: Samra
authors.forename: A J
authors.initials: AJ
authors.lastname: Clark
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics*; D010584:Bacteriophage phi X 174 / Q000235:genetics; D002876:Chromosomes, Bacterial; D004265:DNA Helicases / Q000235:genetics; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics*; D004307:Dose-Response Relationship, Radiation; D004926:Escherichia coli / Q000235:genetics* / Q000528:radiation effects; D029968:Escherichia coli Proteins; D005798:Genes, Bacterial / Q000528:radiation effects; D005819:Genetic Markers; D016296:Mutagenesis; D010641:Phenotype; D011995:Recombination, Genetic; D051716:Replication Protein A; D012097:Repressor Proteins / Q000235:genetics; D012697:Serine Endopeptidases / Q000096:biosynthesis / Q000235:genetics*; D013489:Suppression, Genetic; D014161:Transduction, Genetic; D014466:Ultraviolet Rays; D001616:beta-Galactosidase / Q000096:biosynthesis; D000099160:LexA Repressor Protein
chemical_list: D001426:Bacterial Proteins; D004265:DNA Helicases; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D005819:Genetic Markers; D051716:Replication Protein A; D012097:Repressor Proteins; D012697:Serine Endopeptidases; D001616:beta-Galactosidase; D000099160:LexA Repressor Protein; C071702:DnaC protein, E coli; C053139:sulA protein, E coli