1. Interfaculty Institute of Biochemistry; University of Tübingen; Hoppe-Seyler-Str. 4 72076 Tübingen Germany
2. Max Planck Insitute for Intteligen Systems; Heisenbergstrasse 3 70569 Stuttgart Germany
3. German Cancer Research Center; Im Neuenheimer Feld 280 62120 Heidelberg Germany
4. European Molecular Biology Laboratory (EMBL); Meyerhofstrasse 1 69117 Heidelberg Germany