Just as a pocket watch requires a complex system of gears and springs to keep it ticking precisely, individual cells have a network of proteins and genes that maintain their own internal clock -- a 24-hour rhythm that, in humans, regulates metabolism, cell division, and hormone production, as well as the wake-sleep cycle. Studying this "circadian" rhythm in fruit flies, which have genes that are similar to our own, scientists have constructed a basic model of how the cellular timekeeper works. But now, a new report in this week's issue of the journal Science turns the old model on its...
