A CHROMOSOMALLY ENCODED 2-COMPONENT SENSORY TRANSDUCTION SYSTEM IS REQUIRED FOR VIRULENCE OF AGROBACTERIUM-TUMEFACIENS

TnphoA mutagenesis of Agrobacterium tumefaciens identified new extracy toplasmic protein-encoding virulence loci. Mutations in these loci con ferred increased sensitivity to detergents and several antibiotics. Cl ones carrying these loci were isolated from an A. tamefaciens cosmid l ibrary by complementation of the detergent sensitivities of the mutant s. The locus on one complementing clone was delineated by Tn5 and Tnph oA mutagenesis. DNA sequence analysis of the delineated region reveale d that this locus is made up of two transcriptional units, chvG and ch vI, which were predicted, on the basis of amino acid sequence homology , to encode the members of a two-component sensory transduction system . The membrane-spanning sensor, a histidine protein kinase, was design ated ChvG, and the response regulator, presumably a transcriptional ac tivator, was designated ChvI. Surprisingly, ChvG was also predicted to contain a Walker type A consensus nucleotide binding site, which is u nusual for sensor histidine protein kinases. Site-specific insertion m utations in either chvG or chvI abolished tumor formation ability, as well as the ability to grow on complex media. Neither the genes which are regulated nor the inducing signal is known vet for this system.