GAP into the Breach

Stephen R. Sprang Guanosine triphosphatases (GTPases) are critical regulatory molecules in cells. In this issue, Scheffzek et al. report the structure of the key GTPase Ras complexed with its GAP, an accessory molecule necessary for efficient catalysis. In his Perspective, Sprang compares this new structure with the structure of Gabound to RGS, another important GTPase regulatory system.