Expression of the exoY gene, required for exopolysaccharide synthesis in Agrobacterium, is activated by the regulatory ros gene.

Some mutants of Agrobacterium radiobacter, defective in exopolysaccharide synthesis, were phenotypically complemented by two different regions of cloned chromosomal DNA. One of these had been shown to contain a gene termed ros, a novel class of transcriptional regulator. The other contains a gene termed exoY which encodes a glycosyltransferase that is involved in one of the early steps in exopolysaccharide synthesis. Mutations in ros reduced the expression of exoY and a model to account for the complementation of certain exo alleles by both ros and exoY is presented. TnphoA insertions into exoY which expressed alkaline phosphatase activity were isolated and mapped, confirming the membrane location of the exoY gene product. Some of these mutations were dominant, causing merodiploids to be non-mucoid. exoY is linked to two genes, one encoding an omega-aminotransferase and the other encoding an aldehyde dehydrogenase.