THE NODC PROTEIN OF AZORHIZOBIUM-CAULINODANS IS AN N-ACETYLGLUCOSAMINYLTRANSFERASE

Nod factors are signal molecules produced by Azorhizobium, Bradyrhizob ium, and Rhizobium species that trigger nodule formation in leguminous host plants. The backbone of Nod factors consists of a beta-1,4-N-ace tylglucosamine oligosaccharide from which the N-acetyl group at the no nreducing end is replaced by a fatty acid. The nodABC gene products ar e necessary for backbone biosynthesis. By incubation of cell extracts from Azorhizobium caulinodans with radioactive uridine diphosphate-N-a cetylglucosamine, Nod factor precursors were identified and characteri zed as beta-1,4-N-acetylglucosamine oligosaccharides. By analysis of d ifferent nod gene mutants and by expression of nodC in Escherichia col i, the N-acetylglucosaminyltransferase activity was ascribed to the No dC protein. The results suggest that the first step in biosynthesis of Nod factors is the assembly of the oligosaccharide chain.