1. Whitehead Institute for Biomedical Research (M.R., G.F., B.B., R.J.), Cambridge, Massachusetts 02142;
2. Tupper Research Institute and Department of Medicine (C.F., J.K., R.M.L.), Division of Endocrinology, Diabetes, Metabolism and Molecular Medicine, New England Medical Center, Boston, Massachusetts 02111;
3. Artemis Pharmaceuticals GmbH (R.K.), Cologne, Germany D-51063;
4. Department of Neuroscience (R.M.L.), Tufts University School of Medicine, Boston, Massachusetts 02111;
5. Department of Biology (R.J.), Massachusetts Institute of Technology, Cambridge Massachusetts 02139