Retina-specific kinase involved in the signal turnoff via phosphorylation of rhodopsin (RHO), the G protein- coupled receptor that initiates the phototransduction cascade (PubMed:10097103, PubMed:10704496, PubMed:26427409). This rapid desensitization is essential for scotopic vision and permits rapid adaptation to changes in illumination (PubMed:10097103, PubMed:10704496). May play a role in the maintenance of the outer nuclear layer in the retina (PubMed:26427409). ATP + L-threonyl-[rhodopsin] = ADP + H(+) + O-phospho-L-threonyl-[rhodopsin] ATP + L-seryl-[rhodopsin] = ADP + H(+) + O-phospho-L-seryl-[rhodopsin] Inhibited by RCVRN, which prevents the interaction between GRK1 and RHO (By similarity). Inhibition is calcium-dependent (By similarity). Interacts (via N-terminus) with RCVRN (via C-terminus); the interaction is Ca(2+)-dependent (By similarity). Interacts (when prenylated) with PDE6D; this promotes release from membranes (By similarity). May form a complex composed of RHO, GRK1 and RCVRN in a Ca(2+)-dependent manner; RCVRN prevents the interaction between GRK1 and RHO (By similarity). Subcellular location is not affected by light or dark conditions. Expressed in the retina; primarily located in rod outer segments of retina photoreceptor cells (at protein level) (PubMed:11717351, PubMed:15961391, PubMed:21504899). Also detected in cone photoreceptor cells (at protein level) (PubMed:10704496). Autophosphorylated, Ser-21 is a minor site of autophosphorylation compared to Ser-491 and Thr-492. Phosphorylation at Ser-21 is regulated by light and activated by cAMP. Farnesylation is required for full activity. In rod photoreceptor cells, the light-induced ion currents do not decay rapidly, but are greatly prolonged, contrary to what is observed with wild-type mice. The retina photoreceptor layer appears normal when mutant mice are kept in constant darkness, but exposure to light causes apoptosis in retina photoreceptor cells. Belongs to the protein kinase superfamily. AGC Ser/Thr protein kinase family. GPRK subfamily.