IN-VITRO SULFOTRANSFERASE ACTIVITY OF NODH, A NODULATION PROTEIN OF RHIZOBIUM-MELILOTI REQUIRED FOR HOST-SPECIFIC NODULATION

Early stages of nodulation involve the exchange of signals between the bacterium and the host plant. Bacterial nodulation (nod) genes are re quired for Rhizobium spp. to synthesize lipooligosaccharide morphogens , termed Nod factors. The common nod genes encode enzymes that synthes ize the factor core structure, which is modified by host-specific gene products. Here we show direct in vitro evidence that Rhizobium melilo ti NodH, a host-specific nodulation gene, catalyzes the transfer of su lfate from 3'-phosphoadenosine 5'-phosphosulfate to the terminal 6-O p osition of Nod factors, and we show substrate requirements for the rea ction. Our results indicate that polymerization of the chitooligosacch aride backbone likely precedes sulfation and that sulfation is not abs olutely dependent on the presence or the particular structure of the N -acyl modification. NodH sulfation provides a tool for the enzymatic i n vitro synthesis of novel Nod factors, or putative Nod factor interme diates, with high specific activity.