The response of different KdpD-Usp chimeras to salt stress. Plasmids expressing the indicated proteins were transformed in E. coli HAK006 as reporter strain. Cells were grown in minimal medium containing 5 mM K+ with or without 0.4 M sodium chloride. Cells were harvested in the mid-logarithmic growth phase, and β-galactosidase activity was determined, given in Miller Units . The data are average values obtained from at least three independent experiments, and error bars represent standard deviations.