1. The Randall Institute, King's College London, 26−29 Drury Lane, London WC2B 5RL, United Kingdom, Celltech Therapeutics Ltd., 216 Bath Road, Slough SL1 4EN, United Kingdom, and Laboratory of Molecular Biology, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892−0540