1. MRC Virology Unit, Institute of Virology, Church Street, Glasgow G11 5JR, UK
2. Section of Infection and Immunity, University of Wales College of Medicine, Tenovus Building, Heath Park, Cardiff CF14 4XX, UK
3. Department of Virology, Royal Free and University College Medical School, Royal Free Campus, Rowland Hill Street, Hampstead, London NW3 2QG, UK