1. Department
of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
2. Department
of Chemistry, Northwestern University, Evanston, Illinois 60208, United States
3. Department
of Biochemistry, Brandeis University, Waltham, Massachusetts 02453, United States
4. Department
of Chemistry and Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, United States
5. Howard
Hughes Medical Institute, Cornell University, Ithaca, New York 14853, United States