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Threonine Locus of Escherichia coli K-12: Genetic Structure and Evidence for an Operon

By J. Thèze and I. Saint-Girons


Three genes, thrA, thrB, and thrC, were previously defined and localized in the threonine locus of Escherichia coli K-12. thrA, thrB, and thrC specify the enzymes aspartokinase I-homoserine dehydrogenase I, homoserine kinase, and threonine synthetase, respectively. A complementation analysis of the threonine cluster using derivatives of a lambda phage carrying the threonine genes (λdthrc) demonstrates that: (i) thrB and thrC each consist of a single cistron; and (ii) thrA is composed of two cistrons, thrA1 and thrA2, although it specifies a single polypeptide chain. thrA1 and thrA2 correspond to aspartokinase I and homoserine dehydrogenase I, respectively. Their relative order is established. The demonstration of polar effects of mutations (nonsense or induced by phage Mu) in thrA and thrB is taken as evidence for the existence of a thrA thrB thrC operon, transcribed in this order

Topics: Genetics and Molecular Biology
Year: 1974
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Provided by: PubMed Central
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