RLBP1L1 is a protein of unknown function. It has 45% identity with human CRALBP (Cellular retinaldehyde-binding protein) which carries 11-cis-retinol or 11-cis-retinaldehyde as endogenous ligands and may function as a substrate carrier protein that modulates interaction of these retinoids with visual cycle enzymes. RLBP1L1 is expressed in brain, and several human carcinoma cell lines.