1. Gene Expression Laboratory, the Salk Institute, La Jolla, CA 92037, USA.
2. Abramson Family Cancer Research Institute, Department of Cancer Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
3. Regulatory Biology Laboratory, the Salk Institute, La Jolla, CA 92037, USA.
4. Howard Hughes Medical Institute, the Salk Institute, La Jolla, CA 92037, USA.
5. Molecular and Cellular Biology Laboratory, the Salk Institute, La Jolla, CA 92037, USA.