1. Department of Chemistry and Biochemistry, University of Arizona, Tucson, Arizona 85721, United States
2. Department of Biostatistics, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, United States
3. Department of Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States
4. Genome Center of Wisconsin, University of Wisconsin, Madison, Wisconsin 53706, United States
5. Department of Biomolecular Chemistry, University of Wisconsin, Madison, Wisconsin 53706, United States