title: Identification of multicopy suppressors of the pcnB plasmid copy number defect in Escherichia coli.
abstract: Plasmids containing a ColE1 origin of replication are widely used for cloning purposes in Escherichia coli. Among the host factors that affect the copy number of ColE1 plasmids is the E. coli protein poly(A) polymerase I (PAP I), which regulates the intracellular level of RNA I, a ColE1-encoded negative regulator of plasmid replication. In strains that lack PAP I, RNA I levels are elevated, resulting in reduced levels of ColE1 plasmids in the cell. PAP I is encoded by the gene pcnB. We devised a genetic approach, based on the identification of multicopy suppressor clones, to identify trans-acting factors that can help offset the ColE1 plasmid copy number defect in a pcnB (-) genetic background. Using this strategy, we identified suppressors that mapped to two regions of the E. coli chromosome. The suppressor activity of one of the chromosomal regions was localized to the rssB gene, a response regulator gene known to be involved in the turnover of the stationary-phase sigma factor, RpoS. The second suppressor maps to min 55.4 of the E. coli chromosome, and the factor responsible for the suppressor activity appears to be a novel RNA or protein.
authors.affiliation: Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472, USA.
authors.forename: N
authors.initials: N
authors.lastname: Sarkar
authors.forename: G-J
authors.initials: GJ
authors.lastname: Cao
authors.forename: C
authors.initials: C
authors.lastname: Jain
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics; D003086:Bacteriocin Plasmids / Q000096:biosynthesis / Q000235:genetics*; D001483:Base Sequence; D003001:Cloning, Molecular; D004261:DNA Replication; D004268:DNA-Binding Proteins; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000235:genetics; D016153:Genes, Suppressor; D008957:Models, Genetic; D011062:Polynucleotide Adenylyltransferase / Q000235:genetics*; D013489:Suppression, Genetic; D014157:Transcription Factors
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D014157:Transcription Factors; C098923:rssB protein, E coli; D011062:Polynucleotide Adenylyltransferase; C063643:pcnB protein, E coli