title: The RepA protein of plasmid pSC101 controls Escherichia coli cell division through the SOS response.
abstract: Although plasmid copy number varies widely among different plasmid species, normally copy number is maintained within a narrow range for any given plasmid. Such copy number control has been shown to occur by regulation of the rate of plasmid DNA replication. Here we report a novel mechanism by which the pSC101 plasmid also can detect an imbalance between the cellular level of its replication protein, RepA, and plasmid-borne RepA binding sites to inhibit bacterial DNA replication and delay host cell division when RepA is in relative excess. We show that delayed cell division occurs by RepA-mediated induction of the SOS response and can be reversed by over-expression of the host DNA primase, DnaG. The effects of RepA excess are prevented by introducing a surfeit of RepA binding sites. The mechanism reported here may help to limit variation in plasmid copy number and allow repopulation of cells with plasmids when copy number falls--potentially pre-empting plasmid loss in cultures of dividing cells.
authors.affiliation: Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305-5120, USA.
authors.forename: H
authors.initials: H
authors.lastname: Ingmer
authors.forename: C
authors.initials: C
authors.lastname: Miller
authors.forename: S N
authors.initials: SN
authors.lastname: Cohen
mesh_terms: D001665:Binding Sites; D002455:Cell Division; D002876:Chromosomes, Bacterial / Q000235:genetics / Q000378:metabolism; D004265:DNA Helicases; D019915:DNA Primase / Q000378:metabolism; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000166:cytology* / Q000235:genetics / Q000378:metabolism*; D018628:Gene Dosage; D015964:Gene Expression Regulation, Bacterial; D005838:Genotype; D010957:Plasmids / Q000235:genetics*; D011506:Proteins / Q000235:genetics / Q000378:metabolism*; D013014:SOS Response, Genetics; D015534:Trans-Activators
chemical_list: D004268:DNA-Binding Proteins; D011506:Proteins; D015534:Trans-Activators; C045264:replication initiator protein; D019915:DNA Primase; D004265:DNA Helicases