FIG. 3.

Hybrid sensor kinases with NarX sensor modules and CpxA output modules. The single-letter amino acid sequences of the HAMP linkers of hybrid sensor kinases utilizing the NarX sensor module and the CpxA output module are shown. Sequences from NarX are in plain type; sequences from CpxA are on a gray background; aminoacyl residues not native to either NarX or CpxA used for building the hybrids are boxed. The (arbitrarily assigned) endpoints of AS-1 and AS-2 are denoted by dashed lines, and the coordinates of positions within AS-1 and AS-2 are indicated as in Fig. 1. β-Galactosidase specific activity of the ΔcpxA Φ(cpxP-lacZ) strain VJS7220 expressing the indicated hybrid from a plasmid in the presence (+ NO₃⁻) or absence (− NO₃⁻) of 40 mM NaNO₃ is indicated. Approximately the same β-galactosidase activity was seen for strain VJS7220 carrying an empty plasmid vector as with a plasmid expressing narX (data not shown). For details of culture growth during assays, see Materials and Methods.