Binds a CNS-specific regulatory element of the Dopa decarboxylase (Ddc) gene. Also interacts with sequences adjacent to other transcription units, including Ultrabithorax (Ubx) and engrailed (en). Activity in vivo may be required only at high levels transiently to activate the expression of Ddc in the CNS. Additional isoforms seem to exist. Restricted, during embryogenesis, to tissues derived from ectoderm, predominantly the central nervous system (CNS) and the epidermis. Belongs to the grh/CP2 family. Grainyhead subfamily.