Institution: | a Department of Molecular Biophysics and Biochemistry, Yale University, New Haven, CT 06520-8114, USA b Department of Chemistry, Yale University, New Haven, CT 06520-8114, USA c Schering-Plough Corporation, Kenilworth, NJ 07033-0530, USA d Department of Biochemistry and Molecular Genetics, University of Illinois at Chicago, Chicago, IL 60607, USA |