Human RRH coding sequence and conceptual translation (peropsin) with transmembrane domains (boldface) as predicted by the rod opsin model of Palczewski et al. . The six intron insertion sites in the RRH gene defined in Figure 1 are indicated by black filled circles. Equivalent intron insertion sites for the visual (rod and cone) opsins are indicated by red filled circles – intron positions 1–4 are common to all rod (RHO) and cone opsins, whilst intron 0 is only found in the LWS opsins (OPN1MW, OPN1LW) [13, 17]. The shifted second intron of the pinopsin and VA-opsin families [21, 22] are indicated as 2a and 2b respectively in red circles. Parapineal opsin  and encephalopsin (OPN3)  possess only introns 1, 3 and 4 of the rod and cone opsins. Equivalent intron insertion sites for RGR-opsin (RGR)  are indicated by open circles, whilst those for melanopsin (OPN4)  are indicated by yellow filled circles. Only intron insertion sites 1–7 for melanopsin are indicated due to the extreme length of the melanopsin C-terminus which makes positioning of introns 8 and 9 inaccurate since there is no overlap with any other opsin. Note that intron insertion sites 1 and 4 in RRH are equivalent to intron insertion sites 1 and 4 in RGR.