Fig. 4.

ToxR residues Thr77 and Gln78 are required for full activation of the toxT and ompU promoters. ToxR (wild-type), ToxR-T77A, ToxR-Q78A, or empty vector (pSK) was expressed in V. cholerae ΔtoxR strains harboring either a toxT-lacZ fusion (strain EK1072) or ompU-lacZ (strain EK410) (5). Strains were induced for 3 to 4 h with 100 µM IPTG to express toxR, and β-galactosidase readings were measured. Results are normalized to WT ToxR, set at 100% activation. *P < 0.05 as assessed by Student’s t test. Experiments were performed at least three times in duplicate (n = 6).