My laboratory has isolated and characterized recombinant DNA molecules necessary for the study of the structure and expression of IRBP (Interphotoreceptor Retinoid-Binding Protein). We have cloned many different cDNAs (copies of the IRBP messenger RNA) from bovine and human retina. We have screened a human retina cDNA library with the bovine IRBP cDNA probe and have identified several large cDNA clones up to 3.5 kb in length for human IRBP. We have sequenced portions of all of these overlapping cDNA clones. The IRBP mRNA is long, 4.4 to 7.4 kb in several species and usually gives only one band on a Northern blot. The cDNA and gene sequences have been used to predict the amino acid sequence of the protein. The polypeptide contains four 300 amino acid long repeats, with 30-40% identity among the repeats. These sequences have been helpful in the analysis of the uveitogenic peptides in IRBP. DNA sequence analysis of the gene clone has identified the authentic N-terminus, the putative initiator methionine codon, a putative pro-peptide and a putative signal peptide sequence of the IRBP polypeptide. The chromosomal location of the IRBP gene is: 10 for human, 4 for dog, and 11 for mouse. The bovine gene structure is compact for the size of the protein, and has only 3 introns. The structure of the gene suggests an interesting evolution, involving a processed gene intermediate and two unequal crossovers.
