RsbU phosphatase and RsbT kinase activities are required for full induction of opuCA–lacZ by salt, ethanol or acid stress. (a) NaCl (0.5 M final concentration), (b) ethanol (4 % final, v/v) or (c) acid (pH 5.3 final) stress was imposed on exponentially growing cells at time 0, and β-galactosidase accumulation was assayed at the indicated times. ○, Wild-type strain (PL13); •, rsbT1 (PL14); ▵, sigB : : km (PL17); ▾, rsbUΔ1 (PL15).