Transcriptional regulation by VirR and VirS of members of the Rhodococcus equi virulence-associated protein multigene family.

A virulence plasmid of Rhodococcus equi harbors the vap mutigene family. Here it is shown that transcription of vap gene family members other than vapA (vapD, vapE and vapG) is regulated by temperature and pH and abolished when either virS or virR is deleted. Expression of VirS in the absence of functional VirR was found to increase the transcription of vap genes to the amount expressed in the presence of VirR. These findings suggest that transcription of vap genes is regulated by VirS and that VirR is involved in the mechanism of transcriptional responses to temperature and pH.