Transcription regulator of the gene cluster that mediates the biosynthesis of cercosporin, a light-activated, non-host-selective toxin (PubMed:17462021, PubMed:26938470). The perylenequinone chromophore of cercosporin absorbs light energy to attain an electronically-activated triplet state and produces active oxygen species such as the hydroxyl radical, superoxide, hydrogen peroxide or singlet oxygen upon reaction with oxygen molecules. These reactive oxygen species cause damage to various cellular components including lipids, proteins and nucleic acids (PubMed:11701851). Blocks the expression of the cercosporin cluster and abolishes the production of cercosporin.