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

Forty different single-factor criteria and multi-factor hypotheses about ch ronological order of appearance of amino acids in the early evolution are s ummarized 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 indivi dual rankings by any of the initial criteria. Nine amino acids of the Mille r'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 ord er of appearance of the 20 amino acids on the evolutionary scene also revea ls a unique and strikingly simple chronological organization of 64 codons, that could not be figured out from individual criteria: New codons appear i n descending order of their thermostability, as complementary pairs, with t he complements recruited sequentially from the codon repertoires of the ear lier or simultaneously appearing amino acids. These three rules (Thermostab ility, Complementarity and Processivity) hold strictly as well as leading p osition of the earliest amino acids according to Miller. The consensus chro nology 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 justif ied 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.