Transcription factor binding site diversity within opsin proximal promoters. A - G) Distribution of ten transcription factor binding sites (TFBS) in the proximal promoters of each opsin in O. niloticus and M. zebra. TFBS labelled in blue are present in O. niloticus only, those in red are present in M. zebra only, and those in black are found in both species. Sites labelled simply RAR correspond to all three retinoic acid paralogs. The orientation of factors above or below the central reference line has no special meaning, although O. niloticus-only sites are generally above the line, and M. zebra-only sites are below it. H) Comparison of the average number of binding sites for each transcription factor in the proximal promoters of the opsins and seven randomly-selected, non-opsin genes in O. niloticus. On average, the opsins contain significantly greater numbers of binding sites for these transcription factors compared to the non-opsin genes.