Anticodon and wobble evolution.

The location of the root of life within the Archaea domain close to Methanopyrus kandleri and Aeropyrum pernix on the basis of tRNA sequence clustering has allowed the tracing of evolutionary change in anticodon usages and the wobble rules governing them among different living lineages. Analysis suggests that the primitive Archaea employed simple modes of wobble of anticodon-codon pairing that enable the reading of standard one-amino acid and two-amino acid odon boxes with the uniform use of GNN and UNN anticodons, or the uniform use of GNN, UNN and CNN anticodons, together with the use of a modified C to read the AUA codon of isoleucine. Later on, evolution of tRNA sequences and posttranscriptional modifications brought about in the Bacteria and Eukarya the more complex anticodon usages as described by the Crick Rules of wobble, often with different codon boxes being read with dissimilar anticodon combinations. Still later, the use of a single anticodon to read all four codons in a codon box appeared, both in free living organisms and in organelles. The striking simplicity of the uniform anticodon combinations used by the Archaea to read all standard one- and two-amino acid codon boxes provides strong confirmation for an archaeal root of life.