Shining light on a clock's proteins.

Sunlight defines day and night, and in so doing helps govern the daily activities of plants and animals. Built-in timepieces let plants and animals keep track of the day, but light continually adjusts these biological clocks to keep them accurate. The light-detecting molecules employed by such clocks have remained elusive, however.

Recently, investigators began to suspect that proteins called cryptochromes were the long-sought photoreceptors (SN: 7/11/98, p. 24). Three new reports confirm that suspicion. Together with other proteins that sense red light, cryptochromes that detect blue light govern the daily, or circadian, responses of the weed Arabidopsis thaliana, David E. Somers of the Scripps Research Institute in La Jolla, Calif., and his colleagues report in the Nov. 20 Science. In the Nov. 25 CELL researchers led by Jeffrey C. Hall and Michael Rosbash of Brandeis University in Waltham, Mass., offer evidence that fruit flies with mutations in a cryptochrome gene have altered circadian rhythms. Finally, in the Nov. 20 Science, a research team headed by Aziz Sancar of the University of North Carolina School of Medicine in Chapel Hill reports that among other changes in mice lacking one of two mouse cryptochromes, their biological clocks run on a cycle 1 hour longer than those of normal mice.