Gram negative bacteria such as Vibrio cholera require the production of a number of virulence factors during infection. ToxS, a member of this domain family, is required for ToxR activity. The ToxR and ToxS regulatory proteins are considered to be at the root of the V. cholera virulence regulon, called the ToxR regulon. ToxS serves as a mediator of ToxR function, perhaps by influencing its stability and/or capacity to dimerize, hence ToxS plays an important function in transcriptional activation of Vibrio cholerae virulence genes [1].

1: Virulence regulator AphB enhances toxR transcription in Vibrio cholerae. Xu X, Stern AM, Liu Z, Kan B, Zhu J; BMC Microbiol. 2010;10:3. PMID:20053280