1. Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States
2. Department of Molecular Biology and Genetics, Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, New York 14853, United States
3. Department of Chemistry, Institute for Genomic Biology, and Cancer Center at Illinois, University of Illinois at Urbana-Champaign, 261 Roger Adams Lab Box 36-5, 600 S. Mathews Avenue, Urbana, Illinois 61801, United States
4. Howard Hughes Medical Institute; Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States