In the Sabatini lab, I will explore how cells calibrate their growth, metabolism, and proliferation based on nutrient availability. Cells possess elaborate mechanisms for assessing their nutritional resources and translating that information into the signals that promote or impede their growth. Exactly which food-derived molecules are used to make this decision is a matter of debate. Studies from the Sabatini lab suggest that amino acids—the building blocks of proteins—can activate components in a key signaling pathway central to the regulation of cell growth. However, proteins are not broken down into amino acids in a single step; they are first cleaved to produce peptide fragments that contain a small number of amino acids. Using a suite of techniques in biochemistry, cell biology, and genetics, I will investigate whether peptide fragments, rather than free amino acids, serve as signals for growth modulation. I will explore where in the cell these peptides are generated, how they are transported around the cell, and which of the proteins involved in regulating cell growth detect them—findings that could provide new methods for targeting diseases in which this pathway is dysregulated, including cancer, neurological diseases, and diabetes.