This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Nordström, K. Articles by Lundbäck, A. Search for Related Content PubMed PubMed Citation Articles by Nordström, K. Articles by Lundbäck, A.

 Previous Article  |  Next Article 

J Bacteriol. 1972 May; 110(2): 562-569
Copyright © 1972 American Society for Microbiology. All Rights Reserved.

Mutations in R Factors of Escherichia coli Causing an Increased Number of R-Factor Copies per Chromosome

^a Department of Bacteriology, University of Bristol, The Medical School, University Walk, Bristol BS8 1TD, England, and Department of Microbiology, University of Umeå, S-901 87 Umeå, Sweden

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.

¹ Present address: Department of Microbiology, University of Umeå, S-901 87 Umeå, Sweden.

This article has been cited by other articles:

• Garner, E. C., Campbell, C. S., Mullins, R. D. (2004). Dynamic Instability in a DNA-Segregating Prokaryotic Actin Homolog. Science 306: 1021-1025 [Abstract] [Full Text]  
• del Solar, G., Giraldo, R., Ruiz-Echevarria, M. J., Espinosa, M., Diaz-Orejas, R. (1998). Replication and Control of Circular Bacterial Plasmids. Microbiol. Mol. Biol. Rev. 62: 434-464 [Abstract] [Full Text]