1. Human Cytogenetics Laboratory, Imperial Cancer Research Fund, London, WC2A 3PX, UK
2. Centre for Structural Biology, Imperial College of Science, Technology and Medicine, South Kensington, London, SW7 2AZ, UK
3. Biomolecular Modelling Laboratory, Imperial Cancer Research Fund, London, WC2A 3PX, UK
4. Mathematics and Statistics Group, Imperial Cancer Research Fund, London, WC2A 3PX, UK
5. Molecular Structure Laboratory, Imperial Cancer Research Fund, London, WC2A 3PX, UK