Higher organisms as well as bacteria rely on information on the surrounding environment. In Bacillus sub-tills, diverse extra-cellular stimuli are transformed into an intra-cellular response via a signal integration hub, called the stressosome. The subsequent signal transduction cascade initiates the general stress response (GSR). One of these stimuli is blue light, which is sensed by the bacterial photoreceptor YtvA. We report here-that YtvA is permanently incorporated into the stressosome independent of its illumination state and that RsbT stimulation occurs without direct interaction between the kinase RsbT and YtvA but in a light dependent manner. Furthermore, we show that RsbRA adopts a scaffolding function inside the stressosome explaining on a molecular level why RsbRA is required for light-mediated stress response in vivo. (C) 2013 Elsevier Inc. All rights reserved.