Dr. Lemmon’s laboratory is interested in the sorting and transport of proteins along the endocytic and secretory pathways. Movement along this elaborate membrane system is achieved by the budding, transport, and fusion of membrane vesicles. For years, her lab has studied the structure and function of clathrin, a coat protein used for transport vesicle formation and sorting in the endocytic/endosomal/lysosomal system of all eukaryotic cells. Clathrin is important for down-regulation of many growth-signaling receptors, and thus this pathway of internalization is fine-tuned to the growth needs and environmental cues of the cell. Not surprisingly trafficking in this pathway is perturbed in various forms of cancer at the level of the growth regulating receptors themselves or at the level of the machinery that is involved in receptor sorting, vesicle formation or movement. Thus, knowledge about basic mechanisms of clathrin-mediated transport is essential to understanding the underlying basis of normal growth and cancer. They study clathrin function in S. cerevisiae, a model system where sophisticated molecular and genetic analysis can be applied to address major questions in cell biology, and which has provided important insight onto the molecular mechanisms of many human diseases. Many yeast transport factors are homologues of those found in animal cells, so this has been a powerful system for studying clathrin function. In recent work, the team has studied how endocytosis is regulated by phosphorylation, and they have been investigating endocytic vesicle formation in live cells by following fluorescently tagged endocytic factors. Over 60 proteins are involved in endocytosis, and yeast offers the unique possibility to understand their timing and dynamics and how they affect the mechanics and regulation of endocytic vesicle formation. They are also using yeast to study the biogenesis of the lysosome. This organelle is the major degradative compartment of the cell, where material delivered from the cell surface and autophagy is turned over. Also, the lysosome is a major compartment for ion storage, it is involved in plasma membrane repair, lysosomal enzyme secretion, cell death and cholesterol homeostasis, and it responds to changes in nutrients, such as through TORC signaling. Dr. Lemmon’s team is investigating how membrane proteins on the lysosome-like vacuole of yeast are delivered to maintain this important organelle.