Geremia R A, Mergaert P, Geelen D, Van Montagu M, Holsters M
Laboratorium voor Genetica, Universiteit Gent, Belgium.
Proc Natl Acad Sci U S A. 1994 Mar 29;91(7):2669-73. doi: 10.1073/pnas.91.7.2669.
Nod factors are signal molecules produced by Azorhizobium, Bradyrhizobium, and Rhizobium species that trigger nodule formation in leguminous host plants. The backbone of Nod factors consists of a beta-1,4-N-acetylglucosamine oligosaccharide from which the N-acetyl group at the nonreducing end is replaced by a fatty acid. The nodABC gene products are necessary for backbone biosynthesis. By incubation of cell extracts from Azorhizobium caulinodans with radioactive uridine diphosphate-N-acetylglucosamine, Nod factor precursors were identified and characterized as beta-1,4-N-acetylglucosamine oligosaccharides. By analysis of different nod gene mutants and by expression of nodC in Escherichia coli, the N-acetylglucosaminyltransferase activity was ascribed to the NodC protein. The results suggest that the first step in biosynthesis of Nod factors is the assembly of the oligosaccharide chain.
结瘤因子是由固氮根瘤菌、慢生根瘤菌和根瘤菌属产生的信号分子，可触发豆科宿主植物中的根瘤形成。结瘤因子的主链由β-1,4-N-乙酰葡糖胺寡糖组成，其中非还原端的N-乙酰基被脂肪酸取代。结瘤ABC基因产物是主链生物合成所必需的。通过用放射性尿苷二磷酸-N-乙酰葡糖胺孵育茎瘤固氮根瘤菌的细胞提取物，鉴定出结瘤因子前体并将其表征为β-1,4-N-乙酰葡糖胺寡糖。通过分析不同的结瘤基因突变体以及在大肠杆菌中表达结瘤C，将N-乙酰葡糖胺基转移酶活性归因于结瘤C蛋白。结果表明，结瘤因子生物合成的第一步是寡糖链的组装。
