1. Department of Molecular Biology, The Biomedical Center, Uppsala University, Box 590, S-751 24 Uppsala, Sweden, Institut de Biologie Structurale, 41 Avenue des Martyrs, F-38027 Grenoble Cedex 1, France, European Molecular Biology Laboratory, EMBL c/o DESY, Notkestrasse 85, D-22603 Hamburg, Germany, Institute of Crystallography, Russian Academy of Sciences, Leninsky pr.59, 117333, Moscow, Russia, Department of Molecular and Structural Biology, Aarhus University, Gustav Wieds Vej 10c, DK-8000 Aarhus C,...