Non-chromosomal antibiotic resistance in bacteria. II. Molecular nature of R-factors isolated from Proteus mirabilis and Escherichia coli
摘要：
Covalently closed circular species of R-factor † † Abbreviations used: R-factor, drug resistance factor; RTF, resistance transfer factor (specifies the transfer function of R-factor); R-determinant, specifies drug resistance function of R-factor. DNA have been isolated by Cs 2SO 4Hg 2+ or CsCl-ethidium bromide centrifugation from both Proteus mirabilis and Escherichia coli strains which have been subjected to detergent lysis. In Proteus, the fi + R-factors R1 and R6 consist of at least three independently replicating closed circular species of DNA banding at buoyant densities of 1.709, 1.711 and 1.718 g/cm 3; in E. coli, a single molecular species having a buoyant density of 1.711 g/cm 3 predominates. The respective buoyant densities and calculated molecular weights of isolated R1 and R6 DNA species suggest that the dominant molecular species present in E. coli is the largest of the three forms found in Proteus, and that this species may represent a composite of the two smaller units. Segregants of the R-factor R6 which have lost drug resistance markers but have retained the capacity for transfer have been isolated, and the circular DNA associated with these segregants in both Proteus and E. coli has been characterized by ultracentrifugation and electron microscopy. The results of these experiments suggest that the R6 DNA species banding at ϱ = 1.709 g/cm 3 in Proteus is the transfer unit while the species at ϱ = 1.718 g/cm 3 contains the drug resistance markers. These findings are consistent with a model depicting certain R-factors as being composed of separately replicating, genetically independent units of DNA.
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关键词：
Escherichia coli Proteus Cesium Tritium DNA, Bacterial Microscopy, Electron Ultracentrifugation Molecular Biology Drug Resistance, Microbial DNA Replication
DOI：
10.1016/0022-2836(70)90092-6
被引量：
年份：
1970
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