1. From the Department of Cell Biology (X.G., X.W.), The Scripps Research Institute, La Jolla, Calif; the Departments of Pathology and Pediatrics (D.L.L., J.E.S.), Washington University, St. Louis, Mo; the Department of Physiology (B.G.P., Y.W.), University of Maryland School of Medicine, Baltimore; and the Department of Pharmacology (J.H.B.), University of California, San Diego.