1. Division of Signal Transduction, Beth Israel Deaconess Medical Center, Boston, MA 02115, USA
2. Department of Pathology, Harvard Medical School, Boston, MA 02115, USA
3. EMBL Outstation, European Bioinformatics Institute, Cambridge CB10 1SD, UK
4. Department of Biochemistry, Cambridge University, Cambridge CB2 1QW, UK
5. Department of Marine, Earth and Atmospheric Sciences, North Carolina State University, Raleigh, NC 27695, USA
6. Division of Signal Transduction, Beth Israel Deaconess Medical Center, Boston, MA 02115, USA, Department of Systems Biology, Harvard Medical School, Boston, MA 02115, USA