Chemically selective interactions between nucleotides and amino acids, and their relaionship to features of the genetic code



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The search for selective interactions between nucleic acids and amino acids has for many years been a center of research for a number of scientists. Finding such interactions could give a clue as to some of the steps involved in the evolution of the genetic code. I report here the discovery of these selective interactions as portrayed by the dissociation constants for amino acid methyl ester-nucleotide complexes. Dissociation constants for aromatic amino acids were measured directly whereas those for the non-aromatic amino acid were obtained by allowing the non-aromatic amino acids to compete with tryptophan methyl ester for sites on adenosine nonophosphate (AMP). These selective interactions can be correlated to features of the genetic code - no. of codons, hydrophilicity of the amino acids and coding capacity (defined in text) of the codons. From these correlations a mechanism of primitive coding is proposed. It involves the simultaneous polymerization of amino acids and nucleic acids to polypeptides and polynucleotides. The amino acids with the higher dissociation constants are utilized to a greater extent in the polypeptide sequences. This mechanism holds some validity in the fact that weakly binding amino acids are more highly utilized in forming modern day proteins.