1. Department of Molecular Virology, Immunology, and Medical Genetics, The College of Medicine and Public Health, The Ohio State University, Columbus, Ohio
2. EMBL, Heidelberg, Germany; Institute of Molecular Medicine, University of Freiburg, Freiburg, Germany
3. Zentrum für Molekulare Biologie Heidelberg, Mikrobiologie, Universität Heidelberg, Heidelberg, Germany