title: Regulation of plasmid DNA synthesis: isolation and characterization of copy number mutants of miniR6-5 and miniF plasmids.
abstract: Copy number (Cop) mutants of miniR6-5 and miniF plasmid derivatives containing a beta-lactamase gene were isolated by selection for increased ampicillin-resistance. Mutants which exhibited an increased copy number and a reduced incompatibility response as compared to the respective parent mini-plasmid were obtained from both miniR6-5 and miniF. Characterization of these mutant plasmids has provided the first description of the replicative properties of miniF Cop mutants, and has also facilitated a comparison of plasmids representing the IncFI and IncFII incompatibility groups. Cop mutants from these groups differed in several respects: (i) MiniF Cop mutants were considerably more difficult to obtain and showed a markedly lower transforming efficiency than the corresponding miniR6-5 mutants. (ii) MiniR6-5 Cop mutants were stably maintained in a polA1 strain without selective pressure, whereas miniF Cop mutants severely reduced the viability of this host. (iii) MiniR6-5 replication stopped within a few minutes after inhibition of protein synthesis, whereas miniF replication continued at a declining rate for about one hour in the presence of chloramphenicol. (iv) In contrast to miniR6-5 replication, miniF DNA synthesis was blocked faster by rifampicin than by chloramphenicol. (v) The copy number of miniR6-5 plasmids (but not of miniF) was reduced by about 50% in an rnc strain deficient in RNAase III.
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D002701:Chloramphenicol / Q000494:pharmacology; D004261:DNA Replication; D004269:DNA, Bacterial / Q000096:biosynthesis; D004720:Endonucleases / Q000172:deficiency; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics*; D029968:Escherichia coli Proteins; D005809:Genes, Regulator; D009997:Osmotic Pressure; D010403:Penicillin Resistance; D011815:R Factors; D012093:Replicon; D043244:Ribonuclease III; D012260:Ribonucleases / Q000172:deficiency; D012293:Rifampin / Q000494:pharmacology; D014158:Transcription, Genetic
chemical_list: D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D002701:Chloramphenicol; D000667:Ampicillin; D004720:Endonucleases; D012260:Ribonucleases; D043244:Ribonuclease III; C468366:ribonuclease III, E coli; D012293:Rifampin