Retina-specific kinase involved in the shutoff of the photoresponse and adaptation to changing light conditions via cone opsin phosphorylation, including rhodopsin (RHO). ATP + L-threonyl-[rhodopsin] = ADP + H(+) + O-phospho-L-threonyl-[rhodopsin] ATP + L-seryl-[rhodopsin] = ADP + H(+) + O-phospho-L-seryl-[rhodopsin] Expressed in the eyes (at protein level). Expressed in the eyes, the pineal gland and in the brain. Phosphorylation at Ser-33 is regulated by light and activated by cAMP. Although the protein is present in a diversity of vertebrates ranging from bony fish to mammals, the mouse and rat orthologous proteins do not exist. Belongs to the protein kinase superfamily. AGC Ser/Thr protein kinase family. GPRK subfamily.