1. MRC National Institute for Medical Research, London NW7 1AA, UK.
2. Department of Functional Genomics and Cancer, Institut de Génétique et de Biologie Moléculaire et Cellulaire, 67404 Illkirch Cedex, France.
3. Department of Genetics and Evolution, Jagiellonian University, 30-060 Kraków, Poland.
4. Department of Pathology, Mammalian Molecular Genetics Group, University of Cambridge, Cambridge CB2 1QP, UK.
5. Departments of Surgery and Biology, McGill University, Montreal, QC H3A 1A1, Canada.