VirG

VirG is a transcriptional regulatory protein found in Agrobacterium tumefaciens, central to the control of virulence genes located on the Ti plasmid. It operates as part of the VirA–VirG two-component signaling system that allows the bacterium to respond to plant-derived signals and initiate the transfer of T-DNA into plant cells.

Mechanism and function: VirA functions as a sensor kinase that detects phenolic compounds and other signals released by wounded plant tissue. Upon sensing these cues, VirA phosphorylates VirG. The phosphorylated VirG then binds to promoter regions known as vir boxes upstream of vir gene operons and activates their transcription. This coordinated upregulation includes virB, virD, virE, and related genes, which together assemble the transfer machinery and processing enzymes necessary for T-DNA transfer.

Genetic and structural context: The virG gene resides on the Ti plasmid and encodes a response regulator with the typical architecture of two-component system proteins—an N-terminal receiver domain and a C-terminal DNA-binding domain. Its activity is contingent on phosphorylation by VirA, enabling a rapid transcriptional response to plant cues and contributing to the bacterium’s virulence program.

Broader usage: In biological literature, VirG is most commonly described in relation to the Agrobacterium virulence system. The term may also appear as an acronym or project name in unrelated contexts; when encountered outside this biological framework, the meaning should be clarified by context.

See also: VirA, vir gene cluster, Ti plasmid.