The origin of the genetic code is encrypted in the structure of present-day transfer RNAs

Background/ Objectives: Resolving the origin of the genetic code is fundamental to understanding how life began its journey out of the chemical world. Since its deciphering some 60 years ago, there is still no general theory of the emergence of the genetic code. My objectives are to bring some unique data that might provide some insight into this particular issue. Methods: Because tRNA (transfer RNA) constitutes a crucial piece of the present translational system, having unique structural characteristics, I hypothesized that they might constitute the key elements at the origin of the genetic code and thus decided to compare the primary structure of the tRNAs from a bacterium, Bacillus subtilis. Results: The comparison of the primary structure of the tRNAs from Bacillus subtilis generated a genealogical tree, meaning that the tRNAs were all related and appeared gradually in a precise time sequence. Remarkably, analysis of the various characteristics of this tRNAs tree showed that it very likely reflects the time of entry of amino acids into the Universal Codon Table. Conclusions: These results strongly suggest that the tRNA entity was indeed a major component in the formation of the genetic code and, further, provide a likely scenario for the time sequence of codon colonization of the Universal Codon Table by the various amino acids at the very beginning of life. Also, these data are interpreted in terms of a general theory of the origin of the genetic code I propose, the poly-tRNA theory.