Three-component regulatory mechanism of the H. influenzae HipBA system. (a) Cell-growth analysis showing the effects of expression of different proteins. Each curve represents the growth of cells with a different combination of proteins, as presented within the graph. The data show the average values obtained by triplicate assays; the standard deviations are indicated by error bars. (b) Schematic overview of the presumptive regulatory mechanism according to the interactions between the components of the H. influenzae HipBA system.