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%.

A regulatory mutant, KA600 (ilvC8 livR3 :: TnlO), derepressed in the transport of branched-chain amino acids, was isolated from a strain KA931 (ilvC8) of Salmonella typhimurium LT2, after mutagenesis with tetracycline resistance transposon, Tn10. KA600 still carried P22-phage genome used as a vector in mutagenesis, and when grown on an agar medium, it segregated frequently phage-free clones possessing either a tetracycline-resistance (tetE) or a tetracycline-sensitive (tets) trait. Two of these segregant clones, KA601 (ilvC8 livR3 :: TnlO) and KA602 (ilvC8 livR3), were not different from KA600 in the mode of L-isoleucine transport.Levels of L-isoleucine and L-leucine uptake by KA610 (livR3 :: TnlO), an Ilv+ transductant of KA601, were increased 1.4-to 2.0-fold over those of the wild-type. These uptake abilities were not repressed at all by 5 mM glycyl-L-leucine. Activity of the branchedchain amino acid binding protein (s) of KA602 released by osmotic-shock was several times higher than that of KA931, although the activity of the former was repressible by glycyl-L-leucine to some extent. The livR locus was mapped in the region of 75 to 77 units on the genetic map of S. typhimurium. Nature of livR mutation distinct from a similar regulatory mutation, liv-231 is discussed.