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

Abstract

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-HC1 buffer without MgC12. 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 19 min on the Salmonella genetic map. Co-transduction frequency of livS with aroA, and vice versa, ranged from 12 to 55%.

Location of livA gene participating in the high-affinity transport of branched-chain amino acids in Salmonella typhimurium lt2.

“…When D-xylose was used as a sole carbon source in the minimal medium, Dxylose (5 mg /ml) substituted for glucose (Xylose-minimal medium). When required, following supplements were added to the minimal medium ; L-iso- The livR and livS genes regulate the transport mediated by both the LIV-I and LIV-II systems Murata-Matsubara et al 1985) . leucine (10 pg/ml), L-valine (20 pg/ml), glycyl-L-isoleucine (20 pg/ml), glycyl-L-valine (40 pg/ml), glycyl-L-leucine (20pg/ml), Ca-pantothenate…”