Plays a critical role in the regulation of enzymes involved in nucleotide cycle in photoreceptors (PubMed:21078983, PubMed:27471269). Inhibits the basal catalytic activity and the GCAP-stimulated activity of GUCY2E and GUCY2F, two retinal guanylyl cyclases involved in the production of cGMP in photoreceptors (PubMed:27471269). Involved in the transport of GUCY2E 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 (By similarity). Plays an important role for the survival of rods and cones in the retina (PubMed:8486383, PubMed:17186464). Monomer (By similarity). Interacts with GUCY2E; promotes the exit of GUCY2E from the endoplasmic reticulum and its trafficking to the photoreceptor outer segments (PubMed:21078983). The interaction with GUCY2E negatively regulates its activity (By similarity). Interacts with GUCY2F; promotes the exit of GUCY2F from the endoplasmic reticulum and its trafficking to the photoreceptor outer segments (PubMed:21078983). The interaction with GUCY2F negatively regulates its activity (By similarity). Interacts with GUK1; up-regulates GUK1 activity (By similarity). 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 (PubMed:29515371). Strong dot-like perinuclear staining in the epithelial cells (By similarity). Expressed in the retina and in particular in the inner nuclear layer, in rod and cone outer segments, in the outer nuclear layer, in the outer plexiform layer and in the ganglion cell layer. A spontaneous mutation leading to a frameshift and in an unstable truncated protein lacking the C-terminal 89 amino acids causes retinal degeneration. Homozygotes mice (called rd-3) display retinal degeneration, beginning at 3 weeks of age, characterized by complete loss of photoreceptor rod cells by 5 weeks, and cones by 8 weeks.