FIG. 4.

The Cpx signal transduction system regulates transcription of a cpxP-lacZ fusion situated at the λatt site on the E. coli chromosome. Lanes 1, 3, and 5 show β-galactosidase activities of strains transformed with pBAD18 (control for pND18); lanes 2, 4, and 6 show β-galactosidase activities of strains transformed with pND18 (overexpresses nlpE). Lanes 1 and 2, SP702 (MC4100 ara⁺ zej::Tn10 Δ[pta ackA hisQ hisP] λRS88[cpxP-lacZ]); lanes 3 and 4, SP704 (SP702 cpxA::cam); lanes 5 and 6, SP706 (SP702 cpxR::Ω). All strains were grown in Luria broth containing 0.4% l-arabinose and 50 μg of ampicillin per ml (see Materials and Methods for details). These experiments were performed with strains deleted for pta and ackA. Since NlpE synthesis is driven from the araB promoter (11) in these experiments, full transcriptional induction requires growth in arabinose. Hence, Ac∼P synthesis must be eliminated to prevent hyperphosphorylation of CpxR in the cpxR⁺ cpxA background.