Characterization of the virA gene of the agropine-type plasmid pRiA4 of Agrobacterium rhizogenes.

We sequenced a 4.2-kb DNA region encompassing the vir A locus of the hairy-root-inducing plasmid pRiA4, and compared its sequence with the published vir A region sequences of four tumor-inducing plasmids. An open reading frame capable of coding for 829 amino acids was identified for vir A. Deletion mutants of vir A constructed by fusing to lacZ, but not the wild-type game itself, were efficiently expressed in Escherichia coli when they were put downstream front the lac promoter. These fused gene products became soluble or insoluble depending on the length of their lacZ moieties.