The palindrome dinucleotide-based overlapping of codons and anticodons expected in aa-binding sites of RNA aptamers. Shown on the left is the CG-based similarity of arginine codons (CGN) and anticodons (NCG). Self-complementarity of the CG dinucleotide increases probability of finding codon in an Arg-binding site, if anticodon is already there, and vice versa. The same is the case for four other amino acids that have palindromic dinucleotide-containing codons: AUN (Ile, Met), UAY (Tyr), GCN (Ala). Shown in the middle is a particular codon of arginine, CGC, which, being CG palindrome-containing at 1-2 positions, is simultaneously GC palindrome-containing at 2-3 positions. Accordingly, if the next nt is G, one gets the anticodon with the same palindrome GC at 1-2 positions. Thus, one and the same tetraplet, CGCG, appears as a codon(1-2)/anticodon(2-3) for palindrome CG, and simultaneously as a codon(2-3)/anticodon(1-2) for palindrome GC. In contrast, histidine's codon CAU (shown on the right) has AU palindrome at 2-3 positions only, hence its anticodon (AUG) appears with the same AU at 1-2 positions.