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Carbamoylation of Azorhizobial Nod Factors Is Mediated by NodU

¹Laboratorium voor Genetica, Departement Genetica, Vlaams Interuniversitair Instituut voor Biotechnologie (VIB), Universiteit Gent, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium; ²Laboratoire de Pharmacologie et Toxicologie Fondamentales, Spectrométrie de Masse et Signaux Biologiques, Centre National de la Recherche Scientifique, 205, route de Narbonne, F-31077 Toulouse Cedex, France

Lipochitooligosaccharides (LCOs) synthesized by Azorhizobium caulinodans ORS571 are substituted at the nonreducing-terminal residue with a 6-O-carbamoyl group. LCO biosynthesis in A. caulinodans is dependent on the nodABCSUIJZnoeC operon. Until now, the role of the nodulation protein NodU in the synthesis of azorhizobial LCOs remained unclear. Based on sequence similarities and structural analysis of LCOs produced by a nodU mutant, a complemented nodU mutant, and Escherichia coli DH5α expressing the nodABCSU genes, NodU was shown to be involved in the carbamoylation step.