FUCOSYLATION AND ARABINOSYLATION OF NOD FACTORS IN AZORHIZOBIUM-CAULINODANS - INVOLVEMENT OF NOLK, NODZ AS WELL AS NOEC AND OR DOWNSTREAM GENES/

The DNA region downstream of the nodABCSUIJ operon of Azorhizobium cau linodans was further characterized and two new genes, nodZ and noeC we re identified in the same operon, The A. caulinodans wild-type strain produces a population of Nod factors that, at the reducing end, are ei ther unmodified or carry a D-arabinosyl and/or an L-fucosyl branch, No d factors produced by Tn5-insertion mutants in nodZ, noeC, and the sep arate nolK locus, were analysed by thin-layer chromatography and mass spectrometry, Fucosylation of Nod factors depended on both nodZ and no lK, Arabinosylation depended on noeC and/or downstream genes, Protein extracts of A. caulinodans contained an enzymatic activity for fucose transfer from GDP-fucose to chitooligosaccharides and to Nod factors. By mutant analysis and expression of nodZ in Escherichia cell, the fuc osyltransferase activity was ascribed to the protein encoded by nodZ, In addition, a Nod factor fucosyltransferase activity, independent of nodZ or other known nod genes, was detected in A. caulinodans. Finally , on the basis of sequence similarity of the nolK gene product, and ma ss spectrometric analysis of Nod factors produced by a nolK mutant, we propose that this gene is involved in the synthesis of GDP-fucose.