1. Department of Biochemistry, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
2. Department of Cell Biology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
3. Department of Medical Microbiology & Immunology, University of Alberta, Edmonton, Alberta T6G 2H7, Canada
4. Department of Biochemistry, Microbiology & Immunology, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E5, Canada
5. Li Ka Shing Institute of Virology, Edmonton, Alberta T6G 2E1, Canada