activator [`ak·tǝ´vād·ǝr] CHEMISTRY 1. A substance that increases the effectiveness of a rubber vulcanization accelerator; for example, zinc oxide or litharge. 2. A trace quantity of a substance that imparts luminescence to crystals; for example, silver or copper in zinc sulfide or cadmium sulfide pigments. GENETICS A molecule that modifies a repressor in a way that enables it to stimulate operon transcription. GRAPHIC ARTS See <<accelerator>> |