1. Howard Hughes Medical Institute and Department of Pharmacology, University of Washington School of Medicine, Seattle, Washington 98195;
2. Department of Integrative Biology and Pharmacology, University of Texas Medical School, Houston, Texas 77030
3. The Biotechnology Centre of Oslo and Centre for Molecular Medicine Norway, Nordic European Molecular Biology Laboratory Partnership, University of Oslo, N-0317 Oslo, Norway
4. Department of Infectious Diseases, Oslo University Hospital, N-0424 Oslo, Norway