1. N. Gekakis, A.-M. Delahaye-Brown, C. J. Weitz, Department of Neurobiology, Harvard Medical School, Boston, MA 02115, USA.
2. L. Saez, M. P. Myers, M. W. Young, Howard Hughes Medical Institute, National Science Foundation Science and Technology Center for Biological Timing, and the Laboratory of Genetics, Rockefeller University, New York, NY 10021, USA.
3. A. Sehgal, Department of Neuroscience and the Center for Sleep and Respiratory Neurobiology, University of Pennsylvania Medical Center, Philadelphia, PA 19104, USA.