title: Aminoacyl-tRNA synthetase families and their significance to the origin of the genetic code.
abstract: A correlation of various aspects of the protein structures and substrate and mechanistic specificities of the aminoacyl-tRNA synthetases has led to the identification of at least one family of enzymes probably derived from a common ancestral synthetase. While strong correlations exist only in one part of the array of 64 codons comprising the Genetic Code, this itself may be interpreted as a meaningful pattern, most consistent with a development of the present code from earlier codes containing fewer amino acids and fewer available codons. Specifically, strong correlations in the enzymes whose cognate tRNAs respond to codons containing a central pyrimidine, including the enzyme family of Ile-, Phe-, Val-, Met-, and Leu-tRNA synthetases, suggests that these enzymes evolved last, and that, therefore, an earlier version of the Genetic Code was comprised solely of codons containing a central purine. It is suggested that further study of the historical interrelationships of these enzymes could lead to a fairly detailed picture of how the Genetic Code developed.
mesh_terms: D000604:Amino Acyl-tRNA Synthetases / Q000145:classification / Q000235:genetics*; D003062:Codon; D005815:Genetic Code; D013379:Substrate Specificity
chemical_list: D003062:Codon; D000604:Amino Acyl-tRNA Synthetases