Fernández Mónica, Cuadrado Yolanda, Recio Eliseo, Aparicio Jesús F, Martı N Juan F
Institute of Biotechnology INBIOTEC, Parque Cientı́fico de León, Avda. del Real, no 1, 24006 León, Spain1.
Area of Microbiology, Faculty of Biology, University of León, 24071 León, Spain2.
Microbiology (Reading). 2002 May;148(Pt 5):1413-1420. doi: 10.1099/00221287-148-5-1413.
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.
来自产氨基乙氧基乙烯基甘氨酸（AVG）的链霉菌属菌株NRRL 5331中参与苏氨酸生物合成的三个基因，即hom、thrB和thrC，分别编码高丝氨酸脱氢酶（HDH）、高丝氨酸激酶（HK）和苏氨酸合酶（TS），已被克隆和测序。通过中断实验推断，hom和thrC基因似乎以双顺反子操纵子的形式组织。然而，thrB基因转录为单顺反子转录本。所编码的蛋白质与来自其他细菌物种的HDH、HK和TS蛋白质非常相似。这三个基因的总体组织顺序为hom-thrC-thrB，与其他细菌不同，与天蓝色链霉菌基因组序列中报道的相似。这是首次从链霉菌中对苏氨酸生物合成最后三步的基因簇进行表征。thrC的中断表明，苏氨酸不是链霉菌属菌株NRRL 5331中AVG生物合成的直接前体，并表明该代谢物天冬氨酸衍生生物合成途径的分支点应位于苏氨酸生物合成途径中更早的位置。
