title: Isolation and characterization of ColE1-derived plasmid copy-number mutant.
abstract: The plasmid pBGP120 is a ColE1 derivative that contains elements of the Escherichia coli lac operon and the Tn3 transposon. We have selected and isolated a copy-number mutant of pBGP120. In exponentially growing cultures, the copy-number mutant, pOP1, represents approximately 30% of total intracellular DNA compared to about 5% for pBGP120. Plasmid-encoded beta-galactosidase monomer can represent 50% of newly synthesized protein in cells carrying pOP1. pOP1 is structurally unstable in certain genetic backgrounds and under certain growth conditions, breaking down to a smaller sized plasmid that retains the DNA overproducer phenotype and the Tn3 transposon. The smaller overproducer plasmid, pOP1delta6, is generated by a continuous deletion of sequences located between one end of the Tn3 transposon and a site about 630 nucleotides from the EcoRI site in the beta-galactosidase structural gene of pOP1. pOP1delta6 retains the ColE1 origin of replication but has lost the lac promotor and operator and most of the beta-galactosidase structural gene. pOP1delta6 exists at approximately 210 copies per chromosome in exponentially growing cells.
mesh_terms: D003086:Bacteriocin Plasmids; D001483:Base Sequence; D002872:Chromosome Deletion; D004261:DNA Replication; D004262:DNA Restriction Enzymes; D004269:DNA, Bacterial / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics*; D007763:Lac Operon; D009154:Mutation; D010957:Plasmids; D001616:beta-Galactosidase / Q000235:genetics; D001618:beta-Lactamases / Q000235:genetics
chemical_list: D004269:DNA, Bacterial; D004262:DNA Restriction Enzymes; D001616:beta-Galactosidase; D001618:beta-Lactamases