1. X. Shao and J. Rizo, Department of Pharmacology, and R. B. Sutton, Department of Biochemistry, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75235, USA.
2. B. A. Davletov and T. C. Südhof, Department of Molecular Genetics and Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75235, USA.