FIG 3.

Effects of periplasmic disulfide bonds and cysteine residues on a ToxR-TcpP interaction. (A) ToxR-TcpP interaction in the dsbA mutant. BTH101 and BTH101 ΔdsbA containing pKT25-ToxRS and pUT18C-TcpPH were grown aerobically and anaerobically at 37°C to an OD₆₀₀ of ∼0.3. β-Galactosidase (β-gal) activity was then measured and recorded in Miller units. (B) Effects of periplasmic cysteine mutations. BTH101 containing different combinations of ToxR and TcpP cysteine mutant proteins were grown aerobically and anaerobically at 37°C to an OD₆₀₀ of ∼0.3. β-Galactosidase activity was then measured. (C) Effect of ToxR cysteine mutations on ctx expression in E. coli. E. coli strains containing P_ctxA-luxCDABE reporter and P_lac-toxR (wild type and its cysteine mutant derivatives) plasmids were grown in LB containing 0.5 mM IPTG to an OD₆₀₀ of ∼0.3. Luminescence was then measured and reported as light units/OD₆₀₀ unit. Data represent the mean ± the standard deviation of three independent experiments. WT, wild type.