Target of rapamycin (TOR): balancing the opposing forces of protein synthesis and degradation

Mitogenic and nutritional signals must be integrated for a cell to grow. Th e target of rapamycin (TOR) is emerging as an effector for signals which in dicate to the cell whether the external environment is conducive for growth . Use of the, immunosuppressant rapamycin, a bacterial macrolide, has been instructive in identifying potential signaling components downstream of TOR , leading to the observation that both protein synthesis and turnover are u nder TOR control. The central issues concerning TOR are the identification of the proliferative and anti-proliferative signals which mediate its funct ion and the mechanisms by which these signals are transduced to downstream molecules.