Monitoring Two-Component Sensor Kinases with a Chemotaxis Signal Readout

Bacteria use two-component signal transduction systems to elicit adaptive responses to environmental changes. The simplest of these systems comprises a transmembrane sensor with histidine kinase activity and its cytoplasmic response regulator partner. Stimulus-response studies of two-component signaling systems typically employ expression reporters, such as β-galactosidase, that operate with relatively slow kinetics and low precision. In this chapter, we illustrate a new strategy for directly measuring the signaling activities of two-component sensor kinases in vivo. Our method exploits recent work that defines the recognition determinants for sensor-response regulator signaling transactions, which enabled us to couple histidine kinases to a FRET-based assay that uses signaling components of the E. coli chemotaxis system. We demonstrate the approach with NarX, a nitrate/nitrite sensor kinase, but the method should be applicable to other two-component sensor kinases.