Transfer of TDNA - T-DNA transfer is brought about by the vir region. The vir region is activated by the phenolic signal molecules acetosyringone and α-hydroxyacetosyringone, which are produced by wounded tissues of virtually all dicot plant species, and constitute the wound response.

These molecules bind to the virA gene product, the VirA protein. The VirA acts as a receptor for these signal molecules and becomes activated due to their binding to it. The activated VirA functions as an autokinase and phosphorylates itself. The phosphorylated VirA then phosphorylates Vir G protein, which then, possibly, dimerises and induces the expression of all the 8 vir operons.

Thus the signal phenolic molecules bind to VirA protein which then phosphorylates itself and Vir G protein, a DNA binding protein. Phosphorylated Vir G dimerises, and induces the transcription of all the 8 vir operons. Vir D 1 protein has topoisomerase activity; it binds to the right border sequence and relaxes supercoiling, which facilitates the action of protein VirD2. VirD2 is an endonuclease; it nicks at the right border and covalently binds (and remains bound during the T-DNA transfer) to the 5'-end so generated.