Cells of all living organisms are equipped with complex and interconnected signal transduction pathways enabling them to make appropriate changes in cell growth and metabolism in response to environmental changes. The Functional Biology group has a long-standing tradition in studying the signaling network that allows yeast cells to properly respond to nutritional signals in order to extend cellular lifespan. This project focusses on the protein kinase Sch9 and its central role in nutrient signaling. It is well established that Sch9 receives input from two signaling complexes, the first called TORC1, that senses nutrient availability, and the second called SNF1, that senses the cellular energy levels. However, more recently we found that Sch9 also receives information on the functioning of vacuoles and mitochondria, and that it may control a system allowing for organelle pH management. By acting as integrator of these different signals, it appears that Sch9 can function as molecular switch that opens or closes specific signaling circuits enabling to enhance either nutrient uptake, storage, or recycling, which are all processes that have a major impact on cellular ageing and longevity. We want to understand how this Sch9-dependent molecular switch operates.