1. Department of Biochemistry, University of Alberta, 4-19 Medical Sciences Building, Edmonton, Alberta T6G 2H7, Canada
2. Veterans Medical Research Foundation and the Department of Medicine, University of California, San Diego, 9500 Gilman Drive, Mail Code 0676, La Jolla, California 92093, United States
3. Department of Medical Microbiology and Immunology, Li Ka Shing Institute of Virology, University of Alberta, 1-41 Medical Sciences Building, Edmonton, Alberta T6G 2H7, Canada