Figure 1.

A, Alignment of mouse, rat and human Opn4 deduced amino acid sequences. Residues that are identical in two out the three sequences are shaded. The seven probable transmembrane domains are marked by red lines above the sequence and numbered using roman numerals. The characteristic features of an opsin are shown boxed: lysine (K) to form a Schiff's base at position 337; tyrosine (Y), a possible counterion at position 145; aspartate, arginine, and tyrosine (DRY) tripeptide for transducin binding at position 166–168; and cysteines (C) at positions 142 and 220 for disulfide bridge formation (numbers correspond to the mouse sequence). The intron–exon boundaries are delineated by vertical blue lines and are numbered. The epitopes of the N-terminal antibody (PAS8331) and OPN4L are shown boxed. Accession numbers are as follows: Homo sapiens NM_033282, Rattus norvegicus NM_138860, Mus musculus NM_013887. B, Alignment of amino acids encoded by rat Opn4 exons 9 and 10 with those of the newly identified mouse Opn4S showing that the mouse isoform exon 9 is 8 aa shorter than the rat sequence. Boxes show the epitopes of Opn4S and the C-terminal rat antibody (for more details, see Discussion). C, Amplification of Opn4L and Opn4S coding regions from adult retina cDNA. Products are 1566 bp and 1401 bp. M, Marker (1 kb ladder, Invitrogen); lane 1, no template control for Opn4L primers; lane 2, no template control for Opn4S primers; lane 3, Opn4L; lane 4, Opn4S.