1. Department of Chemistry and Chemical Biology and BioMaPS Institute, Rutgers, the State University of New Jersey, 610 Taylor Road, Piscataway, New Jersey 08854-8066, Lewis-Sigler Institute for Integrative Genomics, Princeton University, Princeton, New Jersey 08544, and Laboratory of Structural Biology, National Institute of Environmental Health Sciences, Research Triangle Park, 12 Davis Drive, Chapel Hill, North Carolina 27709-5900