The function of Ensembl gene identifier ENSG00000198570 (RD3, RD3 regulator of GUCY2D) is as follows. Plays a critical role in the regulation of enzymes involved in nucleotide cycle in photoreceptors (PubMed:21078983, PubMed:21928830, PubMed:27471269, PubMed:29515371, 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). {ECO:0000250|UniProtKB:Q8BRE0, ECO:0000269|PubMed:21078983, ECO:0000269|PubMed:21928830, ECO:0000269|PubMed:27471269, ECO:0000269|PubMed:29515371, ECO:0000269|PubMed:30559291}.