The species-specific features of X. tropicalis NRSEs. A. The most abundant 20 motifs and copy number in the X. tropicalis genome. The asterisk marks the most abundant motif in the humans genome. The green highlight marks the linker region (positions 10 and 11) of the NRSE motif. The red “C” is the only difference between the most abundant NRSE motifs in Xenopus and humans. B. The number of NRSE motif permutations in common between the three vertebrate genomes. C. The consensus motifs derived from the 78 NRSEs in common between humans and X. tropicalis, and the 236 X. tropicalis specific motifs. Arrowheads show the deviations from the X. tropicalis consensus derived from all motifs.