RsbU and RsbT are required for opuCA–lacZ induction by wall-acting antibiotics. (a) Vancomycin (2 μg ml−1 final concentration), (b) bacitracin (20 μg ml−1 final) or (c) nisin (150 μg ml−1 final) was added to exponentially growing cells at time 0. ○, Wild-type strain (PL13); •, rsbT1 (PL14); ▵, sigB : : km (PL17); ▾, rsbUΔ1 (PL15).