Abstract
Ten ilv multisite mutants deficient in both branched-chain-amino-acid aminotransferase and α, β-dihydroxyacid dehydratase activities were isolated from wild-type and ilvD18 strains Salmonella typhimurium LT2. One of these mutants, KA109, harbors an additional deficiency in the activity of the reductoisomerase. From these mutants, five Ile- strains possessing a defect in the branched-chain-amino-acid aminotransferase were isolated by P22 transduction. The TR109 and DT101 strains (Ile-) grow slow and irregular in minimal medium containing isoleucine unless supplementation with leucine and valine in the medium is made. All Ile- strains accumulate α-keto-β-methylvalerate as well as pyruvate and an unknown α-keto acid in the culture media; α-ketoisovalerate and α-ketoisocaproate have not been detected. By mutual and reciprocal cotransduction tests using ilv multisite mutant as recipient and Ile- mutant as donor, an arrangement of the Ile- mutational sites in ilvE locus was obtained.
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