1. Department of Neurology, Northwestern University Medical School, Chicago, IL 60611.
2. Department of Molecular Biology, The Scripps Research Institute, La Jolla, CA 92037.
3. Department of Neurology, Northwestern University Medical School, Chicago, and Northwestern University Institute of Neuroscience, Chicago, IL 60611.
4. Department of Neurology, University of Chicago, Chicago, IL 60637.
5. Department of Neurology, Dent Neurological Institute, Buffalo, NY 14209.
6. Department of Medicine (Neurology), Duke University Medical Center, Durham, NC 27710.
7. Department of Biochemistry, Imperial College, London SW7 2AZ, U.K.
8. Departments of Neurology and of Cell, Molecular, and Structural Biology, Northwestern University Medical School, Chicago, IL 6061 1, and Northwestern University Institute of Neuroscience.