Function of Vir genes

The genes responsible for the transfer of the T-DNA region into the host plant are also situated on the Ti plasmid in a region of approximately 40 kb outside the T-DNA, known as the vir (virulence) region. The genes of vir region are not transferred themselves; they only induce the transfer of T-DNA.

These genes have following functions:

Vir genes	Functions
VirA	Encodes acetosyringone (phenolic sensor) receptor protein, functions as autokinase; also activates VirG gene by phosphorylation leading to constitutive expression of all genes
VirB1-B11	Encodes membrane protein, involved in conjugal tube formation through which T-DNA is transport, VirB11 has ATPase activity
VirC	Encodes helicase enzymes, binds to the overdrive region, unwinding of T-DNA
VirD1	Topoisomerase activity- required for T-DNA processing, modulates VirD2 activity
VirD2	VirD2 is an endonuclease- nicks the right border of T-DNA, directs T-DNA through the VirB/VirD4 transfer apparatus, contain nuclear localization sequences (NLS) that promote nuclear uptake of the T-complex
VirD4	Components of transfer apparatus
VirE1	Required for VirE2 export from Agrobacterium
VirE2	Single strand binding protein (SSBP), binds to T-DNA during transfer, forms a membrane channel that transfers the T-strand through the plant plasma membrane, involved in nuclear targeting and passage through nuclear pore complex, contain nuclear localization sequences (NLS), assist nuclear uptake of the T-complex by keeping the T-strand in an unfolded state
VirF	Directs protein coating of T-DNA complex removal by proteasomal machinery
VirG	Master controller DNA binding protein, vir A activates vir G by phosphorylation, vir G dimerises and activates constitutive expression of all vir operons
VirJ	T-DNA export