Table 1.

The genetic code's 64 codons and their codon directional asymmetry, CDA. Shaded nucleotides indicate the nucleotide at one of the codon's extremities that is the most different from nucleotides at other positions, along rules described in text, and which determines the dominant side of codon directional asymmetry: negative CDA when the first (5′) codon position has the most different nucleotide, and positive CDA when the third (3′) position has the most different nucleotide. Codons assigned to amino acids aminoacylated by class I tRNA synthetases are framed, remaining amino acids are aminoacylated by class II tRNA synthetases.