Mapping of the ros virulence regulatory gene of A. tumefaciens

Virulence functions associated with the oncogenicity of Agrobacterium tumefaciens are encoded by vir genes contained in six major operons located on the Ti plasmid. The virC and virD operons encode functions responsible for host range and T-intermediate processing. These two operons are regulated positively by the product of virG and negatively by the product of the chromosomal gene ros, which encodes a 15.5 kDa repressor. To determine the location of the ros gene we have constructed A. tumefaciens HFR strains, using transposon Tn5mob to mobilize the ros locus, and used them to map the location of ros relative to auxotrophic loci. Tight linkage was found between ros, his-34 and his-19. A linkage map is presented showing the location of ros relative to other known chromosomal genes associated with virulence functions.