News FocusCircadian Rhythms

The Clock Plot Thickens

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Science  16 Apr 1999:
Vol. 284, Issue 5413, pp. 421-422
DOI: 10.1126/science.284.5413.421

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Although many of the components of the circadian clock that regulates our bodily functions over a 24-hour cycle are known to researchers, the crucial photoreceptor that passes light's signal to the clock is not. Now two suspects, the light-sensitive pigments in the rod and cone cells of the mammalian eye, are eliminated by two papers in this issue (pp. 502 and 505). And a report in yesterday's issue of Nature puts an intriguing wrinkle in the story a of another candidate, a protein called cryptochrome, fingering it as a likely part of the clock itself. Its authors found that in mice lacking cryptochrome the clock doesn't run at all, meaning that cryptochrome is essential for clock function, but leaving open the question of whether it is the long-sought circadian photoreceptor in mammals.