Genetic and biochemical studies of livS mutation affecting the regulation of branched-chain amino acid transport in Salmonella typhimurium.

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A mutation livS (livS1 in KA231) that occurred in a Salmonella typhimurium LT2 mutant strain CE5 (ilvC8 brnQ4) expressed pleiotropic effects on cellular characteristics. The mutation not only resulted in derepression of the transport of branched-chain amino acids (Ohnishi et al. 1980), but also altered the properties of the ribosome. Ribosomes of KA2313 (brnQ4 livS1), an Ilv+ transductant of KA231 from the wild-type donor, appeared to be more unstable than those of the ancestral strain KA204 (brnQ4) in a Tris-HCl buffer without MgCl2. When ribosomes of KA2313 were suspended in the buffer, they released substantial amounts of smaller proteins of less than 20, 000 daltons into the buffer, and ribonuclease I was activated. Ribosomes of KA204 liberated a little but much lesser amount of such proteins under the same condition, and ribonuclease I stayed in an inactive state. The livS gene was found to be closely linked to aroA located at 19min on the Salmonella genetic map. Co-transduction frequency of livS with aroA, and vice versa, ranged from 12 to 55%.
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