Characterization of the hom–thrC–thrB cluster in aminoethoxyvinylglycine-producing Streptomyces sp. NRRL 5331 The GenBank accession number for the sequence reported in this paper is AJ312095.

Abstract

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.

Analysis of gene expression in operons of Streptomyces coelicolor

“…Table 1 details known information about the regulation of these genes, where all but one of the OIGs with predicted binding sites are known to have a promoter in their upstream regions. Although formally classified as a monocistronic operon in Streptomyces , thrB is included as it is transcriptionally linked to a bicistronic operon involved in the same pathway immediately upstream in E. coli , and often part of an operon in other organisms (for example, B. subtilis ) [21]. …”

Targeted disruption of homoserine dehydrogenase gene and its effect on cephamycin C production in Streptomyces clavuligerus

“…The deduced amino acid sequence showed 89.8% identity to HSD from aminoethoxyvinylglycine-producing Streptomyces sp. NRRL 5331 [7]. Comparison of the sequence of S. clavuligerus with those of S. avermitilis, S. coelicolor, C. glutamicum, B. subtilis, P. aeruginosa and M. glycogens revealed identities of 89, 87.9, 54.4, 38.4, 36.6 and 31.1%, respectively.…”

“…In Streptomyces, threonine biosynthetic genes hom, thrC (threonine synthase) and thrB (homoserine kinase) are clustered; hom and thrC being organized as a single transcriptional unit while thrB is transcribed as a monocistronic transcript under a strong promoter [7]. Hence, hom disruption in S. clavuligerus was not expected to have any polar eVects other than that on thrC.…”

“…The motif at positions 13 to 18, G-X-G-X-X-G, surrounded by small hydrophobic amino acid residues is the characteristic of the NAD(P)-binding site of HSDs [7,[21][22][23]. Like other HSDs, NAD(P), the cofactor of the enzyme, should bind this region.…”

“…ULM1 [16], Pseudomonas aeruginosa [5], Methylobacillus glycogens [21], Methylobacillus Xagellatus [18], Esherichia coli and Salmonella typhimurium [6] and Streptomyces sp. NRRL 5331 [7].…”