Affiliation: | 1. MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge CB2 0QH, UK;2. University of Cambridge, Department of Medicine, Addenbrooke’s Hospital, Cambridge CB2 0QQ, UK;3. Roslin Institute, University of Edinburgh, Edinburgh EH25 9RG, UK;4. Division of Virology, Department of Pathology, University of Cambridge, Cambridge CB2 0QQ, UK |