Traces in Current Genomes of a Primitive RNA Ring

(1) Background: Previous theoretical studies have provided arguments for the existence of a ring or hairpin RNA that could have served as a primitive informational and functional molecule at the origin of life. The present article consists of searching in current genomes for RNAs closest to this ring in terms of occurrence of similar nucleotide motifs. (2) Methods: In searching for the smallest possible ring/hairpin RNA capable of interacting with amino acids in the construction of the peptides of the primitive living world, we found a circular docosamer RNA molecule (length 22), which we called AL ring (for Alpha or Archetypal Loop). Then, we started to systematically track AL relics in current genomes in the form of motifs like pentamers or pairs of consecutive codons in common with AL. (3) Results: The sequence correspondence between AL and RNA sequences of organisms from different kingdoms of life (Archaea, Bacteria and Eukarya) was found with high statistical significance with a frequency gradient depending on both the antiquity of the species and the functional necessity of the genes. (4) Conclusions: Considering the suitability of AL as a candidate for being a primitive sequence, and the evolution of the different species considered, we can consider the AL RNA ring as a possible actor that favored the appearance of life on Earth.