In the nick of time

Like romance, politics, and batting, cell division requires good timing. Now, a molecular switch that sets the pace for the early part of the cell cycle has been discovered. The switch is novel because it revs up one pathway, while blocking another that may accelerate the cell cycle.

A team led by Richard Assoian of the University of Pennsylvania (Philadelphia, PA) already knew that progression through the cell cycle depended on the protein cyclin D1. Induced during the middle of the G1 phase, cyclin D1 activates a cyclin-dependent kinase that advances the cell through the rest of that phase. Thus, cyclin D1 is vital to the timing of the cell cycle, says Assoian. “We view it as the event that sets the clock for...