RHIZOBIUM-MELILOTI LACKING MOSA SYNTHESIZES THE RHIZOPINE SCYLLO-INOSAMINE IN-PLACE OF 3-O-METHYL-SCYLLO-INOSAMINE

The Rhizobium meliloti Rm220-3 mos locus producing the rhizopine scyll o-inosamine (SI) in nodules is shown to consist of three ORFs (ORF1. m osB and mosC) arranged in an operon structure. This differs from the R . meliloti L5-30 mos locus, which produces 3-O-methyl-scyllo-inosamine (3-O-MSI), by the complete absence of mosA. The deletion covers a reg ion of 1235 nt and includes the entire mosA gene as well as the sequen ce both upstream and downstream. As a result, Rm220-3 mos ORF1 shares a 5' region common with L5-30 ORF1 but includes an additional 10 bp in sertion and a section in the L5-30 mosA and mosB intercistronic region . Antibodies against L5-30 Mos proteins detected MosB and MosC protein s in Rm220-3-induced nodules but no translation product for either ORF 1 or mosA was detected. A construct prepared from the L5-30 mos locus which has a truncated mosA gene produces SI rather than 3-O-MSI, confi rming this gene is involved in a methylation step in the production of 3-O-MSI. Further, changes made to this ORF result in reduced levels o f the rhizopine.