An Activator is a substance that increases the effectiveness of another. For example, a trace quantity of a substance that imparts luminescence to crystals; silver or copper in zinc sulfide or cadmium sulfide pigments. In genetics it would be a molecule that modifies a repressor in a way that enables it to stimulate operon transcription. Examples of activators are: 1-Acetamido-4-cyano-3-methylisoquinoline that is used as a selective inhibitor of cyclic AMP-dependent protein kinase (PKA), while D-erythro-Dihydro-D-sphingosine is used as a Biosynthetic precursor of sphingosine, Inhibits protein kinase C.