1. Interfaculty Institute for Biochemistry, University of Tübingen, D-72076 Tübingen, Germany
2. Division of Virology, Department of Clinical Microbiology, Laboratory for Molecular Infection Medicine in Sweden, Umeå University, SE-901 85 Umeå, Sweden
3. Department of Pediatrics, Vanderbilt University School of Medicine, Nashville, Tennessee 37232