Fig. 6.

Inversion symmetry in the genetic code and in putative sense/antisense coding sequences. (A) Codons and anticodons encode amino acids with complementary physical chemistry (Zull and Smith 1990). Each black line denotes a codon–anticodon pair. Almost without exception, codons for hydrophobic core amino acids in the first two groups have anticodons for amino acids that define surfaces, and vice versa. Codons for proline and glycine include a sense/antisense pair, so that the sequence Pro-Gly, which frequently encodes a turn, is read as Pro-Gly in the reverse direction from the antisense strand. (B) Predictions based on helix-coil transition theory (Muñoz and Serrano 1994; Lacroix et al. 1998) for the two structures shown in figure 1. TrpRS 94-mer predictions (solid circles) are positive. HisRS 94-mer predictions have been multiplied by −1 and plotted in reversed order, C→N.