Plays a critical role in the regulation of enzymes involved in nucleotide cycle in photoreceptors (PubMed:29515371, PubMed:21928830, PubMed:21078983, PubMed:27471269, PubMed:30559291). Inhibits the basal catalytic activity and the GCAP-stimulated activity of GUCY2D and GUCY2F, two retinal guanylyl cyclases involved in the production of cGMP in photoreceptors (PubMed:21928830, PubMed:27471269, PubMed:29515371, PubMed:30559291). Involved in the transport of GUCY2D and GUCY2F to their target sites in the photoreceptor outer segment (PubMed:21078983). Up-regulates the activity of GUK1, a kinase that also plays an essential role for recycling GMP and indirectly, cGMP (PubMed:29515371). Plays an important role for the survival of rods and cones in the retina (By similarity). Monomer (PubMed:30559291). Interacts with GUCY2D; negatively regulates its activity (PubMed:21928830, PubMed:26100624, PubMed:27471269, PubMed:30559291). The interaction with GUCY2D promotes the exit of GUCY2D from the endoplasmic reticulum and its trafficking to the photoreceptor outer segments (PubMed:21078983). Interacts with GUCY2F (By similarity). The interaction with GUCY2F negatively regulates GUCY2F activity (PubMed:29515371). The interaction with GUCY2F promotes the exit of GUCY2F from the endoplasmic reticulum and its trafficking to the photoreceptor outer segments (PubMed:21078983). Interacts with GUK1; up-regulates GUK1 activity (PubMed:29515371). Colocalizes with GUCY2E and GUCY2F in rods and cones photoreceptors. Colocalizes with GUK1 in photoreceptor inner segments and to a lesser extent in the outer plexiform layer (By similarity). Strong dot-like perinuclear staining in the epithelial cells (PubMed:29030614). Expressed in retina (PubMed:12914764). Widely expressed (at protein level) (PubMed:29030614). In the retina the strongest immunoreactivity is detected in the inner half of the cytoplasmic portion of the photoreceptor layer, where rods and cones are found, and the external half of the outer plexiform layer (at protein level) (PubMed:29030614). The disease is caused by variants affecting the gene represented in this entry.