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Characterization of the hom–thrC–thrB cluster in aminoethoxyvinylglycine-producing Streptomyces sp. NRRL 5331

Institute of Biotechnology INBIOTEC, Parque Científico de León, Avda. del Real, no 1, 24006 León, Spain¹
Area of Microbiology, Faculty of Biology, University of León, 24071 León, Spain²

Author for correspondence: Juan F. Martín. Tel: +34 987 210308. Fax: +34 987 210388. e-mail: degjmm{at}unileon.es

Three genes from the aminoethoxyvinylglycine (AVG)-producing Streptomyces sp. NRRL 5331 involved in threonine biosynthesis, hom, thrB and thrC, encoding homoserine dehydrogenase (HDH), homoserine kinase (HK) and threonine synthase (TS), respectively, have been cloned and sequenced. The hom and thrC genes appear to be organized in a bicistronic operon as deduced by disruption experiments. The thrB gene, however, is transcribed as a monocistronic transcript. The encoded proteins are quite similar to the HDH, HK and TS proteins from other bacterial species. The overall organization of these three genes, in the order hom–thrC–thrB, differs from that in other bacteria and is similar to that reported in the Streptomyces coelicolor genome sequence. This is the first time in which the gene cluster for the three last steps of threonine biosynthesis has been characterized from a streptomycete. Disruption of thrC indicated that threonine is not a direct precursor for AVG biosynthesis in Streptomyces sp. NRRL 5331 and suggested that the branching point of the aspartic acid-derived biosynthetic route of this metabolite should lie earlier on the threonine biosynthetic route.

Keywords: threonine biosynthesis, homoserine dehydrogenase, homoserine kinase, vinylglycine, actinomycetes

Abbreviations: AVG, aminoethoxyvinylglycine; HDH, homoserine dehydrogenase; HK, homoserine kinase; PLP, pyridoxal phosphate; TS, threonine synthase

The GenBank accession number for the sequence reported in this paper is AJ312095.

This article has been cited by other articles:

				M. Fernandez, Y. Cuadrado, J. F. Aparicio, and J. F. Martin Role of homoserine and threonine pathway intermediates as precursors for the biosynthesis of aminoethoxyvinylglycine in Streptomyces sp. NRRL 5331 Microbiology, May 1, 2004; 150(5): 1467 - 1474. [Abstract] [Full Text] [PDF]