title: Escherichia coli cells with increased levels of DnaA and deficient in recombinational repair have decreased viability.
abstract: The dnaA operon of Escherichia coli contains the genes dnaA, dnaN, and recF encoding DnaA, beta clamp of DNA polymerase III holoenzyme, and RecF. When the DnaA concentration is raised, an increase in the number of DNA replication initiation events but a reduction in replication fork velocity occurs. Because DnaA is autoregulated, these results might be due to the inhibition of dnaN and recF expression. To test this, we examined the effects of increasing the intracellular concentrations of DnaA, beta clamp, and RecF, together and separately, on initiation, the rate of fork movement, and cell viability. The increased expression of one or more of the dnaA operon proteins had detrimental effects on the cell, except in the case of RecF expression. A shorter C period was not observed with increased expression of the beta clamp; in fact, many chromosomes did not complete replication in runout experiments. Increased expression of DnaA alone resulted in stalled replication forks, filamentation, and a decrease in viability. When the three proteins of the dnaA operon were simultaneously overexpressed, highly filamentous cells were observed (>50 micro m) with extremely low viability and, in runout experiments, most chromosomes had not completed replication. The possibility that recombinational repair was responsible for the survival of cells overexpressing DnaA was tested by using mutants in different recombinational repair pathways. The absence of RecA, RecB, RecC, or the proteins in the RuvABC complex caused an additional approximately 100-fold drop in viability in cells with increased levels of DnaA, indicating a requirement for recombinational repair in these cells.
authors.affiliation: Department of Biology, San Diego State University, California 92182-4614, USA.
authors.forename: Aline V
authors.initials: AV
authors.lastname: Grigorian
authors.forename: Rachel B
authors.initials: RB
authors.lastname: Lustig
authors.forename: Elena C
authors.initials: EC
authors.lastname: Guzmán
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Mahaffy
authors.forename: Judith W
authors.initials: JW
authors.lastname: Zyskind
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism; D005434:Flow Cytometry; D007544:Isopropyl Thiogalactoside / Q000494:pharmacology; D008954:Models, Biological; D009154:Mutation; D009876:Operon; D011995:Recombination, Genetic / Q000235:genetics*; D013014:SOS Response, Genetics
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C066312:DnaA protein, Bacteria; D029968:Escherichia coli Proteins; C489340:recF protein, E coli; D007544:Isopropyl Thiogalactoside; C066218:recF protein, Bacteria