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18 July 1997
Vol 277, Issue 5324

About The Cover

Complex between the guanosine triphosphate (GTP)-binding protein Ras and the GTPase-activating protein GAP, showing an arginine residue from GAP (red chain) complementing the active site of Ras (brown chains) with its essential glutamine residue. This "arginine-finger" in the active site stabilizes the transition state of the GTP hydrolysis reaction, mimicked by guanosine diphosphate and aluminum fluoride (green), and enhances the reaction rate by several orders of magnitude. See 333 and the Perspective on 329. [Graphics: Frank Schmitz]