THE CHROMOSOMAL VIRULENCE GENE, CHVE, OF AGROBACTERIUM-TUMEFACIENS ISREGULATED BY A LYSR FAMILY MEMBER

Certain plant phenolic compounds and monosaccharides induce the transc ription of virulence (vir) genes of Agrobacterium tumefaciens through the VirA-VirG two-component regulatory system. The product of the chro mosomal virulence gene chvE is homologous to galactose-binding protein of Escherichia coli and is required for vir gene induction by sugars. Adjacent to, but divergent in transcription from, chvE is an open rea ding frame, now termed gbpR (galactose-binding protein regulator), tha t is homologous to the LysR family of transcriptional regulators. chvE =lacZ expression was induced by L-arabinose, D-galactose, and D-fucose when gbpR was present. In the absence of inducer, GbpR repressed chvE =lacZ expression. In addition, GbpR negatively regulated its own expre ssion.