Marchenko George N, Marchenko Natalia D, Tsygankov Yuriy D, Chistoserdov Andrei Y
Institute of Genetics and Selection of Industrial Micro-organisms, 1st-Dorozhniy pr. 1, Moscow, Russia1.
Marine Sciences Research Center, State University of New York at Stony Brook, Stony Brook, NY 11794-5000, USA2.
Microbiology (Reading). 1999 Nov;145 ( Pt 11):3273-3282. doi: 10.1099/00221287-145-11-3273.
The genes encoding aspartate kinase (ask), homoserine dehydrogenase (hom), homoserine kinase (thrB) and threonine synthase (thrC) from the obligate methylotroph Methylobacillus flagellatus were cloned. In maxicells hom and thrC directed synthesis of 51 and 48 kDa polypeptides, respectively. The hom, thrB and thrC genes and adjacent DNA areas were sequenced. Of the threonine biosynthesis genes, only hom and thrC were tightly linked in the order hom-thrC. The gene for thymidylate synthase (thyA) followed thrC and the gene for aspartate aminotransferase (aspC) preceded hom. All four genes (aspC-hom-thrC-thyA) were transcribed in the same direction. mRNA analysis indicated that hom-thrC are apparently transcribed in one 7.5 kb transcript in M. flagellatus. Promoter analysis showed the presence of a functional promoter between aspC and hom. No functional promoter was found to be associated with the DNA stretch between hom and thrC. The thrB gene encoded an unusual type of homoserine kinase and was not linked to other threonine biosynthesis genes.
对专性甲基营养菌鞭毛甲基杆菌中编码天冬氨酸激酶（ask）、高丝氨酸脱氢酶（hom）、高丝氨酸激酶（thrB）和苏氨酸合酶（thrC）的基因进行了克隆。在最大细胞中，hom和thrC分别指导合成51 kDa和48 kDa的多肽。对hom、thrB和thrC基因以及相邻的DNA区域进行了测序。在苏氨酸生物合成基因中，只有hom和thrC紧密连锁，顺序为hom-thrC。胸苷酸合酶（thyA）基因位于thrC之后，天冬氨酸转氨酶（aspC）基因位于hom之前。所有四个基因（aspC-hom-thrC-thyA）都朝同一方向转录。mRNA分析表明，在鞭毛甲基杆菌中，hom-thrC显然在一个7.5 kb的转录本中被转录。启动子分析表明，在aspC和hom之间存在一个功能性启动子。未发现与hom和thrC之间的DNA片段相关的功能性启动子。thrB基因编码一种不寻常类型的高丝氨酸激酶，且不与其他苏氨酸生物合成基因连锁。
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