1. Biological Sciences Collegiate Division, The University of Chicago, Chicago, Illinois 60637, USA
2. Division of Biological Sciences, The University of Chicago, Chicago, Illinois 60637, USA
3. Department of Biochemistry and Molecular Biology, The University of Chicago, Chicago, Illinois 60637, USA
4. James Franck Institute, The University of Chicago, Chicago, Illinois 60637, USA
5. Material Measurement Laboratory, Material Science and Engineering Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
6. Departments of Pathology, Biochemistry, and Molecular Biology, The University of Chicago, Chicago, Illinois 60637, USA