1. *Department of Molecular Biophysics and Biochemistry,
2. Department of Cell Biology, The Scripps Research Institute, La Jolla, CA 92037; and
3. Department of Biological Sciences, Vanderbilt University, Nashville, TN 37235
4. Department of Neurobiology, and
5. Interdepartmental Neuroscience Program, Yale University, New Haven, CT 06511;