[Demonstration of 3 functional domains responsible for a kinase activity in VirA, a transmembrane sensory protein encoded by the Ti plasmid of Agrobacterium tumefaciens].

High-level expression of chimeric virA genes were obtained by replacing the first codons of virA with the first codons of trpE. The fusion proteins encoded by these constructs were partially purified and one of them exhibited autokinase activity. Therefore, protein phosphorylation may be an important feature of VirA function. This allowed us to define the existence of three functional domains inside VirA.