Alignment of opsin sequences. Alignment of a subset of c-opsins (yellow) and r-opsins (blue) shows sites with conserved amino acid residues specific for c-opsins (yellow shading) and r-opsins (blue shading). Green horizontal bars indicate transmembrane regions I to VII, blue horizontal bars indicate extracellular domains (ECDI-ECDIII), red horizontal bars indicate intracellular domains (ICDI-ICDIII) and a black horizontal bar indicates a region believed to interact with G-protein. Cv marks the site believed to harbour the counter ion (glutamic acid, E) residue in vertebrates  and Ci for invertebrates . An asterisk marks the residue lysine (K) that binds the retinal. Bta 113, Bta 181, Bta 296 and asterisks indicate the bovine opsin numbering system. Different grey-scale shadings indicate the percentage of amino acids identical at the given position, black = 100%, dark grey = at least 90%, light grey = at least 75%.