1. Department of Neurobiology, Anatomy and Cell ScienceUniversity of Pittsburgh School of MedicinePittsburghPennsylvania15261USA
2. Departments of Biochemistry and Chemistry and of Protein and Molecular BiologyRoyal Free Hospital School of MedicineRowland Hill StreetNW3 2PFUnited Kingdom
3. Department of Cellular and Molecular SciencesSt. George's Hospital Medical SchoolCranmer TerraceLondonSW17 OREUnited Kingdom