1. Howard Hughes Medical Institute–Gordon and Betty Moore Foundation, Watson School of Biological Sciences, Cold Spring Harbor Laboratory, 1 Bungtown Road, Cold Spring Harbor, NY 11724, USA.
2. Ottawa Institute of Systems Biology, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada.
3. Howard Hughes Medical Institute, Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016, USA.
4. Feinberg School of Medicine, Department of Molecular Pharmacology and Biological Chemistry, Northwestern University, Chicago, IL 60611, USA.
5. Department of Biology, Indiana University, 915 East Third Street, Bloomington, IN 47405, USA.
6. Institut de Biologie de l’École Normale Supérieure, 75005 Paris, France.