Transcription factor that binds and transactivates the sequence 5'-TAATC[CA]-3' which is found upstream of several photoreceptor-specific genes, including the opsin genes. Acts synergistically with other transcription factors, such as NRL, RORB and RAX, to regulate photoreceptor cell-specific gene transcription. Essential for the maintenance of mammalian photoreceptors (By similarity). Interacts (via the homeobox) with NRL (via the leucine-zipper domain). Interacts with PDC, RAX2, RORB and SCA7 (By similarity). Retina. Belongs to the paired homeobox family.