A REGULATORY TRANSPORT MUTANT FOR BRANCHED-CHAIN AMINO ACIDS IN SALMONELLA TYPHIMURIUM

Abstract

A new regulatory mutant, KA231 (ilvC8 brnQ4 liv-231), derepressed in the transport of branched-chain amino acids was isolated from a transport-defective mutant, CE5 (ilvC8 brnQ4) of Salmonella typhimurium LT2. Kinetic analysis of isoleucine and leucine transports indicated that activities of the high-affinity and the low-affinity-(1) systems of KA2313, an Ilv⁺ transductant of KA231, were increased 1.3- to 2.5-fold over the levels of KA204 (brnQ4). The activity of specific binding protein(s) found in the periplasmic space of KA2313 cells was also increased several-fold. Glycyl-L-leucine was able to repress both the transport and the binding activities of KA2313, but the extent of repression was weaker than that of repression induced in wild-type strain. Nature of liv-231 mutation distinct from another regulatory mutation, gleR, is discussed.