1. Department of Physiology, University of California, San Francisco, California, USA;
2. Current affiliation: Structural Biology Program, Memorial Sloan Kettering Cancer Center, New York, New York, USA
3. Current affiliation: Department of Biology, Stanford University, Palo Alto, California, USA
4. Department of Biochemistry and Biophysics, University of California, San Francisco, California, USA;
5. Howard Hughes Medical Institute, University of California, San Francisco, California, USA