1. Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037
2. Department of Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037
3. Current address: University of California, San Diego Skaggs School of Pharmacy and Pharmaceutical Sciences 9500 Gilman Drive, La Jolla, California 92093
4. Current address: Biocenter Oulu and Department of Biochemistry, University of Oulu, PO Box 3000, FIN-90014 Oulu, Finland
5. Division of Medicinal Chemistry, Leiden/Amsterdam Center for Drug Research, PO Box 9502, 2300RA Leiden, The Netherlands
6. Department of Molecular Physiology and Biological Physics, University of Virginia Health System, PO Box 800736, Charlottesville, Virginia 22908-0736