1. Department of Plant & Microbial Biology, University of California, Berkeley, CA 94720
2. Department of Bacteriology, University of Wisconsin–Madison, Madison, WI 53706
3. Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94304
4. QB3/Chemistry Mass Spectrometry Facility, University of California, Berkeley, CA 94720
5. Molecular Biophysics and Integrated Bioimaging Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720