Köplin R, Arnold W, Hötte B, Simon R, Wang G, Pühler A
Lehrstuhl für Genetik, Universität Bielefeld, Germany.
J Bacteriol. 1992 Jan;174(1):191-9. doi: 10.1128/jb.174.1.191-199.1992.
The nucleotide sequence of a 3.4-kb EcoRI-PstI DNA fragment of Xanthomonas campestris pv. campestris revealed two open reading frames, which were designated xanA and xanB. The genes xanA and xanB encode proteins of 448 amino acids (molecular weight of 48,919) and 466 amino acids (molecular weight of 50,873), respectively. These genes were identified by analyzing insertion mutants which were known to be involved in xanthan production. Specific tests for the activities of enzymes involved in the biosynthesis of UDP-glucose and GDP-mannose indicated that the xanA gene product was involved in the biosynthesis of both glucose 1-phosphate and mannose 1-phosphate. The deduced amino acid sequence of xanB showed a significant degree of homology (59%) to the phosphomannose isomerase of Pseudomonas aeruginosa, a key enzyme in the biosynthesis of alginate. Moreover, biochemical analysis and complementation experiments with the Escherichia coli manA fragment revealed that xanB encoded a bifunctional enzyme, phosphomannose isomerase-GDP-mannose pyrophosphorylase.
野油菜黄单胞菌野油菜致病变种的一个3.4 kb EcoRI - PstI DNA片段的核苷酸序列显示有两个开放阅读框，分别命名为xanA和xanB。xanA和xanB基因分别编码含448个氨基酸（分子量为48,919）和466个氨基酸（分子量为50,873）的蛋白质。通过分析已知参与黄原胶产生的插入突变体鉴定出了这些基因。对参与UDP - 葡萄糖和GDP - 甘露糖生物合成的酶活性进行的特异性测试表明，xanA基因产物参与了1 - 磷酸葡萄糖和1 - 磷酸甘露糖的生物合成。xanB推导的氨基酸序列与铜绿假单胞菌的磷酸甘露糖异构酶（藻酸盐生物合成中的关键酶）有显著的同源性（59%）。此外，生化分析以及用大肠杆菌manA片段进行的互补实验表明，xanB编码一种双功能酶，即磷酸甘露糖异构酶 - GDP - 甘露糖焦磷酸化酶。
