1. Departments of Medicine and Cell Biology (R.N.D., T.C.V., J.F.E., C.F.B.), University of Virginia Health Sciences Center, Charlottesville, Virginia, 22908
2. W.M. Keck Center for Cellular Imaging (A.P.), Department of Biology, University of Virginia, Charlottesville, Virginia 22904
3. Metabolic Research Unit and Department of Medicine (F.S.), University of California, San Francisco, California 94143-0540