title: The mechanism of recA polA lethality: suppression by RecA-independent recombination repair activated by the lexA(Def) mutation in Escherichia coli.
abstract: The mechanism of recA polA lethality in Escherichia coli has been studied. Complementation tests have indicated that both the 5'-->3' exonuclease and the polymerization activities of DNA polymerase I are essential for viability in the absence of RecA protein, whereas the viability and DNA replication of DNA polymerase I-defective cells depend on the recombinase activity of RecA. An alkaline sucrose gradient sedimentation analysis has indicated that RecA has only a minor role in Okazaki fragment processing. Double-strand break repair is proposed for the major role of RecA in the absence of DNA polymerase I. The lexA(Def)::Tn5 mutation has previously been shown to suppress the temperature-sensitive growth of recA200(Ts) polA25::spc mutants. The lexA(Def) mutation can alleviate impaired DNA synthesis in the recA200(Ts) polA25::spc mutant cells at the restrictive temperature. recF+ is essential for this suppression pathway. recJ and recQ mutations have minor but significant adverse effects on the suppression. The recA200(Ts) allele in the recA200(Ts) polA25::spc lexA(Def) mutant can be replaced by delta recA, indicating that the lexA(Def)-induced suppression is RecA independent. lexA(Def) reduces the sensitivity of delta recA polA25::spc cells to UV damage by approximately 10(4)-fold. lexA(Def) also restores P1 transduction proficiency to the delta recA polA25::spc mutant to a level that is 7.3% of the recA+ wild type. These results suggest that lexA(Def) activates a RecA-independent, RecF-dependent recombination repair pathway that suppresses the defect in DNA replication in recA polA double mutants.
authors.affiliation: Department of Cell Biology, University of New Mexico Health Sciences Center, Albuquerque 87131, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Cao
authors.forename: T
authors.initials: T
authors.lastname: Kogoma
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D004254:DNA Nucleotidyltransferases / Q000378:metabolism; D004256:DNA Polymerase I / Q000378:metabolism; D004260:DNA Repair; D004261:DNA Replication; D004926:Escherichia coli / Q000235:genetics*; D005804:Genes, Lethal; D019426:Integrases; D009154:Mutation; D014176:Protein Biosynthesis; D011938:Rec A Recombinases / Q000235:genetics / Q000378:metabolism; D045522:Recombinases; D011995:Recombination, Genetic; D018085:Regulon; D012697:Serine Endopeptidases; D013696:Temperature; D000099160:LexA Repressor Protein
chemical_list: D001426:Bacterial Proteins; D004254:DNA Nucleotidyltransferases; D004256:DNA Polymerase I; D019426:Integrases; D011938:Rec A Recombinases; D045522:Recombinases; D012697:Serine Endopeptidases; D000099160:LexA Repressor Protein; C115006:integron integrase IntI1