1. QB3 Institute, Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA.
2. Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA.
3. Department of Biology, Institute of Molecular Systems Biology, ETH Zurich, 8093 Zurich, Switzerland.
4. Department of Chemistry, University of California, Berkeley, CA 94720, USA.
5. Faculty of Science, University of Zurich, Zurich, Switzerland.
6. Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA.