1. Department of Infectious Diseases, University of Heidelberg, 69120 Heidelberg, Germany;
2. Bavarian NMR Center, Department of Chemistry, Technical University of Munich, 85748 Garching, Germany
3. Institute of Structural Biology, Helmholtz Zentrum München, 85764 Neuherberg, Germany
4. Division of Virus-Associated Carcinogenesis, German Cancer Research Center (DKFZ), 69120 Heidelberg, Germany