PHOTORECEPTOR RIM PROTEIN - PARTIAL SEQUENCES OF CDNA SHOW A HIGH-DEGREE OF SIMILARITY TO ABC TRANSPORTERS

Purpose. To isolate and sequence cDNA for bovine rim protein, a large membrane-bound glycoprotein found in photoreceptor outer segments. Met hods. Bovine rim protein was N-terminally sequenced (22 residues) and fragments were prepared by partial proteolysis. Two internal sequences of 21 and 18 amino acid residues were obtained from 35 kDa and 32 kDa fragments, respectively. Sense and anti-sense oligonucleotide primers were constructed, based on the peptide sequences derived from the 35 kDa and 32 kDa fragments, respectively, and the polymerase chain react ion (PCR) was used to amplify a 150 bp sequence from bovine retinal cD NA. Results. The amplified sequence coded for the remainder of the pep tide sequence determined from the 35 kDa fragment, which was not prese nt in the primer, confirming that it was derived from the rim protein. The 150 bp sequence was translated to give a 50 amino acid peptide. P art of this peptide was compared with Dna sequence databases using the TFastA program, which found 94.6% identity with an EST derived from h uman retina and 86.1% identity to the mouse abc1 transporter. Conclusi ons. It is proposed that rim protein is a member of the ATP transporte r family of proteins. It may be involved in transport of molecules inv olved in visual transduction across the photoreceptor disk membrane.