1. Howard Hughes Medical Institute, Jack H. Skirball Center for Chemical Biology and Proteomics, The Salk Institute for Biological Studies, La Jolla, California 92037, United States
2. Department of Cell and Molecular Biology, Uppsala University, BMC Box 596, S-751 24 Uppsala, Sweden
3. Department of Chemistry−BMC, Uppsala University, BMC Box 576, S-751 23 Uppsala, Sweden
4. Department of Molecular Physiology and Biomedical Engineering, University of Virginia, Charlottesville, Virginia 22903, United States
5. Department of Biomolecular Sciences, The Weizmann Institute of Science, Rehovot 76100, Israel
6. Department of Chemistry, University of Texas at Austin, Austin, Texas 78712, United States