Exhibits transcriptional activation activity. Positive regulator of light-regulated genes, probably being a direct downstream target of COP1 for mediating light control of gene expression. Interacts with COP1. Triggered by light. Repressed by COP1 in darkness. Defects in light-dependent anthocyanin and chlorophyll accumulation, as well as defects in the light control expression of light-inducible genes involved in anthocyanin biosynthesis and photosynthesis.