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The recovery of tryptophan A auxotrophs at high frequency in a strain of Salmonella typhimurium

Published online by Cambridge University Press:  14 April 2009

S. Riyasaty
Affiliation:
Department of Genetics, Trinity College, Dublin
G. W. P. Dawson
Affiliation:
Department of Genetics, Trinity College, Dublin
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1. Auxotrophs were sought in a slow-growing reversion of the tryA47 strain of S. typhimurium. This reversion differs from tryA47 by a genetic change that is inseparable from the 47 site and has been designated 47S. Out of thirty-nine auxotrophs that derived from independent mutations, twenty-two grew on minimal medium supplemented with anthranilic acid. Eight of these auxotrophs were examined and each was shown to have the 47S site unchanged and to carry a further mutation in the tryA gene. These further mutations were shown to be at different sites in different auxotrophs.

2. Auxotrophs were sought in the wild-type LT-2 strain. None out of thirty-six were mutant in the tryA gene.

3. The 47S site in tryA47S was replaced by 47+ transduced from wild-type LT-2. Auxotrophs were sought in this strain and only one out of nineteen was mutant in the tryA gene.

4. Auxotrophs were sought in a wild-type reversion of tryA47. Out of twenty-six none were mutant in the tryA gene.

5. The 47+ site in wild-type LT-2 was replaced by 47S transduced from tryA47S. Auxotrophs were sought in this strain and twenty-two out of fifty-five were mutant in the tryA gene.

6. We conclude that tryA auxotrophs are only recovered at a high frequency when the 47S site is present in the tryA gene.

7. In strains with the 47S site in the tryA gene the frequency of auxotrophs that will grow on minimal medium supplemented with indole but not on minimal medium supplemented with anthranilic acid is appreciably higher than in those strains without the 47S site in the tryA gene. These auxotrophs are mutant in genes that are in the same operon as tryA.

Type
Research Article
Copyright
Copyright © Cambridge University Press 1967

References

Davis, B. D. (1948). Isolation of biochemically deficient mutants in bacteria by means of penicillin. Proc. natn. Acad. Set. U.S.A. 35, 110.Google Scholar
Ito, J. & Yanofsky, C. (1966). The nature of the anthranilic acid synthetase complex of Escherichia coli. J. biol. Chem. 241, 41124114.Google ScholarPubMed
Riyasaty, S. & Dawson, G. W. P. (1967). A genetic study of primary and secondary reversions of some tryptophan auxotrophs of Salmonella typhimurium. Genet. Res. 9, 269282.CrossRefGoogle Scholar
Smith-Keary, P. F. (1960). A suppressor of leucineless in Salmonella typhimurium. Heredity, Lond. 14, 6171.CrossRefGoogle Scholar
Smith-Keary, P. F. & Dawson, G. W. P. (1964). Episomic suppression of phenotype in Salmonella. Genet. Res. 5, 269281.CrossRefGoogle Scholar
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