1. AG Neurochemie, Institut für Biochemie, Freie Universität Berlin, Thielallee 63, D-14195 Berlin, Germany, Protein & Peptide Group, European Molecular Biology Laboratories (EMBL), Meyerhofstrasse 1, D-69117 Heidelberg, Germany, and Protein Interaction Laboratory, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, Denmark