FIG 4.

Effect of Ca²⁺ and TC on TcpP-TcpP interaction. E. coli cells harboring the adenylate cyclase two-hybrid constructs for TcpP or ToxR were grown microaerobically until reaching mid-log phase and then assessed for β-galactosidase activity, reported in Miller Units. (A) TcpP interaction in the presence of 1 mM TC, 10 mM CaCl₂, or both together. (B) ToxR interaction in the presence of 1 mM TC, 10 mM CaCl₂, or both together. Data shown are from three independent experiments. *, P < 0.05 (Student t test).