Evolution of the genetic code. Why are there strong and weak letter   doublets? The first gene, the first protein. Early (ancient) biosynthesis of   protein
  The idea of the evolution of the genetic code from the CG to the CGUA alphabet has been developed further. The assumption of the originally triplet structure of the genetic code has been substantiated. The hypothesis of the emergence of stop codons at the early stage of the evolution of the genetic code has been additionally supported. The existence of strong and weak letter doublets of codons and the symmetry of strong doublets in the genetic code table, discovered by Rumer, have been explained. A hypothesis concerning the primary structure of the first gene and the first protein has been proposed. 
Denis A. Semenov