1. Department of Biochemistry and Molecular Biology, The University of Chicago, 929 East 57th Street, Chicago, Illinois 60637
2. Department of NanoBiophotonics, Max Planck Institute for Biophysical Chemistry, 37070 Göttingen, Germany
3. Department of Molecular Genetics and Cell Biology, The University of Chicago, 920 East 58th Street, Chicago, Illinois 60637