title: Mutations in R factors of Escherichia coli causing an increased number of R-factor copies per chromosome.
abstract: A mutant of the repressed R factor R1a and two mutants of the derepressed R factor R1drd-19 showing a two- to fourfold increase in resistance to all of the antibiotics to which the wild-type R factors mediate resistance were studied. The increased resistance was due to a two- to fourfold increase in the number of R-factor copies per chromosome. The production of drug-metabolizing enzymes was linearly correlated to the gene dosage. There was also a linear correlation between resistance to the drugs and the production of the corresponding enzymes. The mutations were also expressed in Proteus mirabilis PM1. In Proteus, R factors are split into two plasmids, resistance transfer factor and the resistance part. The mutation in one of the mutant R factors seems to be located in the resistance part. A second fi(+) R factor (R100) was introduced into strains already carrying R1drd-19 or the mutant R factor R1drd-19B2. In the first case, R100 and R1drd-19 segregated with equal probability when the bacteria were grown on antibiotic-free medium, whereas, in the second case, R100 was rapidly and preferentially excluded.
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D002499:Centrifugation, Density Gradient; D002586:Cesium; D002712:Chlorides; D002876:Chromosomes, Bacterial; D004269:DNA, Bacterial / Q000032:analysis; D004352:Drug Resistance, Microbial; D004798:Enzymes / Q000378:metabolism; D004926:Escherichia coli / Q000032:analysis / Q000187:drug effects* / Q000201:enzymology / Q000254:growth & development; D004996:Ethidium; D005827:Genetics, Microbial; D008826:Microbial Sensitivity Tests; D009154:Mutation; D011513:Proteus mirabilis / Q000187:drug effects; D013395:Sucrose; D013936:Thymidine; D014316:Tritium
chemical_list: D000900:Anti-Bacterial Agents; D002712:Chlorides; D004269:DNA, Bacterial; D004798:Enzymes; D014316:Tritium; D002586:Cesium; D013395:Sucrose; D004996:Ethidium; D013936:Thymidine