EXPRESSION OF THE EXOY GENE, REQUIRED FOR EXOPOLYSACCHARIDE SYNTHESISIN AGROBACTERIUM, IS ACTIVATED BY THE REGULATORY ROS GENE

Some mutants of Agrobacterium radiobacter, defective in exopolysacchar ide synthesis, were phenotypically complemented by two different regio ns of cloned chromosomal DMA. One of these had been shown to contain a gene termed res, a novel class of transcriptional regulator. The othe r 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 accoun t for the complementation of certain exo alleles by both ros and exoY is presented. TnphoA insertions into exoY which expressed alkaline pho sphatase activity were isolated and mapped, confirming the membrane lo cation 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 aldeh yde dehydrogenase.