Members of the superfamilies of molecular motors, kinesins, dyneins and myosins, are the machines that drive many forms of crucial intracellular transport. The three motor families coordinate their actions with dynamic (and highly regulated) cytoskeletal filaments to control cell growth, define cell shape, deliver and polarize intracellular cargoes, traffic endosomal membranes, and participate in signaling cascades. Many critical cellular processes involve the regulated switching of cargo organelles from one type of cytoskeletal filament to another, but the requisite coordination and competition among multiple motors are not understood. This integrated program project will study the interactions, structure, regulation, and biophysical mechanisms of the molecular motors in growing and functioning cells. The cytoskeletal tracks for intracellular motility, actin and microtubules, the actin-based motors, myosin I, myosin V, and the microtubule-based motors, cytoplasmic dynein and kinesin, will be studied intensively using a battery of state-of-the-art approaches that open exciting research opportunities. Single-molecule fluorescence polarization, nanometer-resolved fluorophore localization, infrared optical traps, rapid biochemical reaction kinetics, genetic manipulations, and novel forms of electron microscopy, correlated with hyper-resolution light microscopy in the same regions, will be applied in collaborative studies to understand the mechanisms of individual molecular motors and their mutual interactions. These approaches yield high temporal and spatial resolution that enables us to dissect mechanisms in assays of increasing molecular complexity that model aspects of the intracellular environment. Particular biological systems, selected for facility of study as well as relevance to broader mechanisms of intracellular motility are endocytosis and vesicle trafficking in neurons and insulin-stimulated fusion of glucose transporter vesicles with the surface membrane in adipocytes. There are close synergies and practical links between all of the sections and cores in this program. We anticipate that the proposed work will take us significantly further toward our goal of understanding motility in the normal and pathological function of cells.