1. Howard Hughes Medical Institute and Department of Cellular & Molecular Pharmacology, University of California, San Francisco, California 94143, United States
2. Graduate
Program in Chemistry and Chemical Biology, University of California, San
Francisco, California 94158, United States
3. Department
of Physiology, University of California, San Francisco, California 94158, United States
4. Department
of Chemistry, University of California, Berkeley, California 94720, United States