Recent advances in molecular biology have shown GTPases and phosphoproteins to be the paramount molecular switches uti- lized intracellularly in biological systems. The origins of the GTPase switch appear to be almost as ancient as life it- self, and through evolution nature has adapted this switch to a variety of purposes. In this two-volume work a broad survey of the major classes of GTPases is presented. The role of GTPases in ensuring ac- curacy during protein translation, a new look at the trimeric G-protein cycle, the molecular function of ARF in vesicle coating, the emerging role of...