1. Max Planck Institute of Molecular Cell Biology and Genetics, 01307 Dresden, Germany
2. Research Institute, Division of Molecular Structure and Function, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada
3. Institut für Virologie, Medizinische Fakultät Carl Gustav Carus, Technische Universität Dresden, 01062 Dresden, Germany
4. Department of Biochemistry and Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario M5S 1A1, Canada