Gene Recruitment for a Subunit of Isopropylmalate Isomerase
The leucine Operon in Salmonella typhimurium consists of four structural genes, leuABCD (Burns et al., 1966; Margolin, 1963), and a control region located adjacent to the leuA gene. The major regulation of the expression of the leucine Operon occurs via modulation of the transcription attenuation of a leader region that responds to the intracellular level of leucyl-tRNAleu (Gemmill et al., 1979; Wessler and Calvo, 1981). In addition, mutations at a locus flr unlinked to the leucine operon result in constitutive expression of the leucine genes as well the isoleucine/valine gene (Fried-berg et al., 1974). The relationship of the leucine genes to the enzymes in the leucine biosynthetic pathway is shown in Fig. 1. The enzymes α-isopropylmalate synthetase (leuA gene product) and β-isopropylmalate dehydrogenase (leuB gene product) have been purified from S. typhimurium and characterized (Kohlhaw et al., 1969; Parson and Burns, 1970). The work described here is particularly concerned with the second leucine biosynthetic enzyme, isopropylmalate isomerase.
KeywordsMutant Strain Enzyme Subunit leuA Gene Leucine Biosynthesis leuA2010 Mutation
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