1. Sanger Institute, Wellcome Trust Genome Campus, Hinxton, Cambridge, CB10 1SA, UK.
2. Department of Microbiology and Immunobiology, School of Medicine, Queen's University of Belfast, Grosvenor Road, Belfast, BT12 6BN, UK.
3. Institute of Cell and Molecular Biology, University of Edinburgh, Darwin Building, Kings Buildings, Edinburgh EH9 3JR, UK.
4. Department of Molecular and Cell Biology, University of Cape Town, Private Bag Rondebosch 7701, South Africa.
5. Division of Medical Microbiology, University of Edinburgh Medical School, Teviot Place, Edinburgh, EH8 9AG, UK.