CpxR directly binds the T6SS2 hcp2B promoter region of APEC. A The sequence and schematic representation of the hcp2B promoter region. The bold line shows the sequence used in the lacZ fusion and EMSA analyses. The putative CpxR binding site is indicated with boxes. The putative −35 and −10 elements of the promoter are indicated with underlining. B EMSA for the binding of CpxR-P protein to the hcp2B promoter region. The hcp2B promoter DNA fragment with or without the CpxR binding site was amplified and biotin-labeled, and the biotin-labeled probe was mixed with increasing amounts of CpxR-P protein. For the specific competitive EMSA, CpxR-P protein was incubated with both the biotin-labeled and the unlabeled DNA probes. The biotin-labeled DNA was detected with a chemiluminescent substrate. The concentrations of CpxR-P protein and probes are shown below the figure.