1. J. D. Plautz and S. A. Kay, Department of Cell Biology and National Science Foundation Center for Biological Timing, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
2. M. Kaneko and J. C. Hall, Department of Biology and National Science Foundation Center for Biological Timing, Brandeis University, Waltham, MA 02254, USA.