1. Gene Therapy and Molecular Virology Group, John P. Robarts Research Institute, London, Ontario, N6A 5K8 Canada
2. Bureau of Microbiology, Canadian Science Centre for Human and Animal Health, Winnipeg, Manitoba, R3E 3R2 Canada
3. Division of Neurology, Department of Medicine,University of British Columbia,Vancouver,British Columbia, V6T 2B5, Canada
4. National Cancer Institute, National Institutes of Health, Frederick, Maryland 21701
5. Department of Zoology, Brigham Young University, Provo, Utah 84602