Relationship between RGD-like motifs in human, baboon, mouse and rat PSG N domains. The font size used for each tri-peptide motif represents relative abundance among the PSG proteins, and the codon sequences are shown underneath. Arrows represent single or double (x2) transitions (ts) or transversions (tv) as indicated. Motifs and codon sequences in grey type are intermediates that have not been observed in vivo. Primate RGD-like motifs cluster naturally in the left-hand box, whereas those of the rodents cluster in the right-hand box. The baboon derived PAE motif is an outlier and is bracketed.