Consensus temporal order of amino acids and evolution of the triplet code

Forty different single-factor criteria and multi-factor hypotheses about chronological order of appearance of amino acids in the early evolution are summarized in consensus ranking. All available knowledge and thoughts about origin and evolution of the genetic code are thus combined in a single list where the amino acids are ranked chronologically. Due to consensus nature of the chronology it has several important properties not visible in individual rankings by any of the initial criteria. Nine amino acids of the Miller's imitation of primordial environment are all ranked as topmost (G, A, V, D, E, P, S, L, T). This result does not change even after several criteria related to Miller's data are excluded from calculations. The consensus order of appearance of the 20 amino acids on the evolutionary scene also reveals a unique and strikingly simple chronological organization of 64 codons, that could not be figured out from individual criteria: New codons appear in descending order of their thermostability, as complementary pairs, with the complements recruited sequentially from the codon repertoires of the earlier or simultaneously appearing amino acids. These three rules (Thermostability, Complementarity and Processivity) hold strictly as well as leading position of the earliest amino acids according to Miller. The consensus chronology of amino acids, G/A, V/D, P, S, E/L, T, R, N, K, Q, I, C, H, F, M, Y, W, and the derived temporal order for codons may serve, thus, as a justified working model of choice for further studies on the origin and evolution of the genetic code. (C) 2000 Elsevier Science B.V. All rights reserved.