Molecular characterization of the virulence gene virG of pTiKU 12.

The virulence (vir) genes of Agrobacterium tumefaciens KU12, a Korean strain, were not induced by acetosyringone and the strain showed weak tumor forming ability and broad plant host ranges. We identified complete nucleotide sequence of virG of pTiKU12, an octopine Ti plasmid of this strain. When it was compared with those of other Ti plasmids, pTiKU12 virG contained an open reading frame (ORF) of 726 nucleotides which showed much lower homology (about 77%) than those (above 98%) already known among octopine Ti plasmids and it started with GTG codon instead of TTG found in other Ti plasmids. Only two vir boxes and one promoter region were confirmed in 5'-untranslated region instead of three vir boxes and two promoters which were found in pTiA6 virG. Nevertheless, important amino acids for the functional activity of VirG were so conserved that the virG included in pUCDG could complement a virG mutant Agrobacterium tumefaciens Mx19 in beta-galactosidase activity assays and on plant tumor tests.