Stimulation of the vvhA gene by ToxRSVv in an E. coli background. Compatible plasmid pJL961 carrying the 3.4-kb vvhA gene fragment was cotransformed with a plasmid carrying toxRSVv (pCMM601), toxRVv (pCMM610), toxRSVc (pCMM641), or toxRVc (pCMM651) under the control of the PBAD promoter. (A) Hemolytic activity in the culture supernatant was assayed at the indicated time intervals. Cultures were induced with 0.2% arabinose. Each error bar indicates the standard error of the mean of triplicate experiments. Symbols: ×, pJL961 only; □ and ■, pCMM601 before and after induction, respectively; ▵ and ▴, pCMM610 before and after induction, respectively; ○ and ● with solid line, pCMM641 before and after induction, respectively; ○ and ● with broken line, pCMM651 before and after induction, respectively. (B) ToxRVv levels in the bacterial cells were measured by Western blot analysis. Top, pCMM610 after induction; bottom, pCMM601 after induction. The numbers above the photographs are the times after induction.