1. Interdepartmental Neuroscience Program, Yale University School of Medicine, New Haven, Connecticut 06536, Institute for Systems Biology, 4225 Roosevelt Way NE, Suite 200, Seattle, Washington 98105-6099, and Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, 405 Mary Ellen Jones Building, Campus Box 7260, Chapel Hill, North Carolina 27599-2852