1. Department of Molecular Biology, J5, Central Institute of Mental Health, 68159 Mannheim, Germany, Department of Neurobiology, University of Heidelberg, INF 364, 69120 Heidelberg, Germany, Department of Biological Research, Boehringer Ingelheim KG, 55126 Ingelheim, Germany, and Laboratory for Alzheimer's Disease Research, Adolf-Butenandt-Institute, Ludwig-Maximilians-University, 80336 Munich, Germany