Characterization of the virE operon of the Agrobacterium Ti plasmid pTiA6

The Agrobacterium tumefaciens Ti plasmid contains at least six transcriptional units (designated vir loci) which are essential for efficient crown gall tumorigenesis. Mutations in one of these loci, virE, result in a sharply attenuated virulence phenotype. In the present communication, we have analyzed the virE operon at the molecular level. This locus contains open reading frames coding for two hydrophilic proteins having molecular weights of approximately 7,000 daltons and 60,500 daltons. Using a maxicell strain of E. coli, we have visualized two proteins encoded by virE which correspond in size to these open reading frames. Analysis of codon usage of virE and seven other vir loci indicates that, in contrast to E. coli, all possible codons for a given amino acid are utilized at approximately the same frequency.