1. Department of Immunology and Molecular Pathology, University College London, Gower Street, London, WC1E 6BT, UK. E-mail: P.Kellam@ucl.ac.uk
2. Department of Information Systems and Computing, Brunel University, Uxbridge, Middlesex, UB8 3PH, UK. E-mail: Xiaohui.Liu@brunel.ac.uk, Stephen.Swift@brunel.ac.uk, Allan.Tucker@brunel.ac.uk
3. Department of Computer Science, Birkbeck College, Malet Street, London, WC1E 7HX, UK. E-mail: Nigel@dcs.bbk.ac.uk
4. Department of Biochemistry and Molecular Biology, University College London, Gower Street, London, WC1E 6BT, UK. E-mail: C.Orengo@biochemistry.ucl.ac.uk