1. Department of Neurology, David Geffen School of Medicine, Brain Research Institute, and Molecular Biology Institute, University of California, Los Angeles, California 90095, Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106, Center for Polymer Studies, Department of Physics, Boston University, Boston, Massachusetts 02215, and Center for the Study of Systems Biology, School of Biology, Georgia Institute of Technology, Atlanta, Georgia 30318