Evolutionary Pathway of the Genetic Code deduced based on Coevolution Theory

The coevolution theory suggests that origin and evolution of the genetic code proceed along with development of synthetic pathway of amino acids. The coevolution theory is undoubtedly a correct idea, because the genetic code could not evolve, if synthetic pathways of new amino acids were not invented and the new amino acids did not accumulate at a large amount in the cells. On the other hand, studies on metabolic pathways have progressed and information about metabolic pathways obtained thus far has been stored in KEGG PATHWAY Database. Then, amino acid metabolic pathways were analyzed in detail in order to answer to the following questions. (1) The genetic code originated from what type of genetic code? (2) The genetic code has reached to the universal genetic code, passing through what type of intermediate genetic code, SNS code or RNY code? From the results, it could be reconfirmed that the genetic code originated from the GNC primeval genetic code and evolved to the universal genetic code passing through SNS genetic code. Lastly, limits and future prospects of the coevolution theory are also discussed.