Identification of Regulatory Elements in a Conserved Upstream Region of the Gene Encoding Interphotoreceptor Retinoid-Binding Protein (IRBP)

Abstract

(First Paragraph) IRBP is a large, single-subunit extracellular glycolipoprotein found in the interphotoreceptor matrix between the photoreceptor cells and retinal pigment epithelium cell layer (Fig. 1.). The protein is synthesized and secreted by the photoreceptor rods and cones, as well as pinealocytes, of all vertebrates. The molecular weight of human IRBP (1230 residues) is 133,400 daltons. This protein consists of four homologous segments of approximately 300 residues each. Each segment contains highly conserved hydrophobic domains among species. Ligands identified as bound to IRBP include retinoid isomers and fatty acids, and IRBP can also bind cholesterol, a-tocopherol and retinoic acid. The ability of IRBP to bind various retinoid isomers, fatty acids and many other hydrophobic ligands suggests multiple functions in the retina .