1. Wellcome Centre for Cell Biology, University of Edinburgh, Edinburgh EH9 3BF, UK.
2. Gene Center Munich, Ludwig-Maximilians-Universität München, 81377 Munich, Germany.
3. Protein Analysis Unit, Biomedical Centre Munich, Faculty of Medicine, Ludwig-Maximilians-University, 82152 Munich, Germany.
4. Department of Structural Biology, Max Planck Institute of Biochemistry, D-82152 Martinsried, Germany.
5. Institute of Biotechnology, Technische Universität Berlin, 13355 Berlin, Germany.