TRANSCRIPTIONAL CONTROL OF TOXT, A REGULATORY GENE IN THE TOXR REGULON OF VIBRIO-CHOLERAE

Co-ordinate expression of many virulence genes in Vibrio cholerae is u nder the control of the ToxR and ToxT proteins. These proteins functio n in a regulatory cascade in which ToxR is required to activate toxT, and ToxT activates virulence genes. The precise mechanism for ToxR act ivation of toxT is unknown, but data presented in this report suggest a direct involvement of ToxR. Primer extension and gene fusion analyse s identified a ToxR-regulated promoter directly upstream of toxT, imme diately following a region of inverted repeats capable of terminating transcription. Gel mobility shift studies indicate that ToxR binds DNA within the inverted repeat region, yet preliminary evidence suggests that ToxR binding alone is not sufficient for activation of toxT. Poss ible mechanisms of ToxR-dependent toxT expression are discussed.