1. Max Delbrueck Center for Molecular Medicine, D-13125 Berlin, Germany; Massachusetts General Hospital, Charlestown, MA 02129; Lilly Research Laboratories, Indianapolis, IN 46285; Department of Neurological Sciences, Rush University Medical Center, Chicago, IL 60612; Institute of Medical Biochemistry, University of Aarhus, DK-8000 Aarhus, Denmark; and Department of Pathology, University of Melbourne, Melbourne, Victoria 3010, Australia