Stimulus–response characteristics of the stressosome. The different stimuli used in experiments by Marles-Wright et al. (2008)  were ethanol (triangles) and NaCl (circles). The simulations according to the three models tested are: product activation (continuous line), substrate activation (dashed line), no cooperation (dashed-dotted line). As experiment and simulation use different stimuli (NaCl, ethanol and kphr, respectively), and response definitions (β-galactosidase and RsbS phosphorylation) the stimuli and responses were normalised according to Equation 1. Ethanol and NaCl activate the stressosome in an identical manner, leading to identical stimulus–response characteristics. Only the product activation model approximates the experimentally observed sigmoidal character of this response. The parameters are identical to the reproduction of the Kim et al. (2004)  data and are shown in Tables 1 and 3.