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Evidence that there are two types of determinant for tetracycline resistance among R-factors

Published online by Cambridge University Press:  14 April 2009

E. C. R. Reeve
E. C. R. Reeve
Affiliation:
Institute of Animal Genetics, West Mains Road, Edinburgh EH9 3JN, Scotland

Summary

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A series of derepressed mutants of the tetracycline resistance (T) determinant in R-factor R57 have been found to be repressor-negative and recessive to the T determinant in R6. It is shown that these (Tdr) mutants are dominant to the inducible T determinant in RPl, indicating that the T determinants in R57 and RP1 code for different repressors of the resistance gene. The same Tdr determinants are unstable in cells carrying both the R57 mutant and RP1, probably due to selection against the dominant Tdr gene because it depresses the growth rate of the host cell compared with its T+ homologue. It is suggested that the T determinants giving high-level resistance in R57, R6 and R100 form one homologous group, probably disseminated by the transposon TnlO, while T determinants giving a much lower level of resistance, such as that in RP1, form a separate group, which may include those in R46, and R199. It is proposed that the gene responsible for tetracycline resistance should be designated tetA and the repressor gene tetI. The R57 Tdr mutants then have the genotype tetI−tetA+.

Type
Research Article
Information
Genetics Research , Volume 31 , Issue 1 , February 1978 , pp. 75 - 84
Copyright
Copyright © Cambridge University Press 1978

References

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