title: Allele-specific suppression of ColE1 high-copy-number mutants by a rpoB mutation of Escherichia coli.
abstract: We have isolated spontaneous rifampicin-resistant mutants from Escherichia coli that showed allele-specific suppression of the copy-number phenotype of ColE1 high-copy-number mutants in vivo. The key step in the regulatory circuitry of the initiation of ColE1 DNA replication is the formation of the persistent hybrid between the primer RNA and the DNA template around the replication origin. Three host-encoded enzymes, RNase H, DNA polymerase I, and RNA polymerase, are essential to the replication initiation in vitro. To decide whether the activity of RNA polymerase is involved directly in the formation of the persistent hybrid, we screened rifampicin-resistant colonies for suppressors of ColE1 copy-number mutants. Suppressor strain YY572 (rpoB572) changes the 572 residue of the beta subunit of RNA polymerase, encoded by the rpoB gene, from isoleucine to leucine. Another suppressor, YY513 (rpoB513), changes the 513 residue from glutamine to lysine. The other known rifampicin-resistant alleles located at residue 513, rpoB8 and rpoB101, did not show a significant suppression of the copy number of those ColE1 copy-number mutants as rpoB513. The suppression by rpoB513 on different ColE1 copy-number mutants showed allelic specificity. The possible roles of RNA polymerase in control of ColE1 copy number are discussed.
authors.affiliation: Program in Molecular, Cellular, and Developmental Biology, Department of Biology, Indiana University, Bloomington, Indiana, 47405, USA.
authors.forename: Y L
authors.initials: YL
authors.lastname: Yang
authors.forename: B
authors.initials: B
authors.lastname: Polisky
mesh_terms: D000483:Alleles; D012321:DNA-Directed RNA Polymerases / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics*; D018628:Gene Dosage; D016153:Genes, Suppressor; D009154:Mutation; D010641:Phenotype; D010957:Plasmids / Q000235:genetics*; D014161:Transduction, Genetic
chemical_list: D012321:DNA-Directed RNA Polymerases; C105078:RNA polymerase beta subunit