Inhibits the transcriptional activation activity of the cone-rod homeobox CRX (By similarity). May participate in the regulation of visual phototransduction or in the integration of photoreceptor metabolism. Interacts with CRX (By similarity). Forms a complex with the beta and gamma subunits of the GTP-binding protein, transducin. Light-induced changes in cyclic nucleotide levels modulate the phosphorylation of this protein by cAMP kinase. Defects in PDC are the cause of photoreceptor dysplasia (PD); an autosomal recessive disease of miniature schnauzer dogs causing retinal degeneration. Belongs to the phosducin family.