PAS, Present, and Future: Clues to the Origins of Circadian Clocks

Circadian clocks are everywhere. These molecular time-keeping devices are found in the cells and tissues of all organisms, including single-cell life forms and plants. In this issue Crosthwaite et al . (p. [763][1]) report a key molecular component, WC-2, of the circadian clock from the fungus Neurospora , which contains one of the best understood clocks. In his Perspective Kay discusses the fact that WC-2 is also a light-receiving molecule and how this lets us understand for the first time the evolutionary origins of circadian clocks. [1]: http://www.sciencemag.org/cgi/content/short/276/5313/763