A possible evolutionary process of emergence of life based upon the GADV hypothesis is as follows. [GADV]-amino acids were synthesized on the primitive Earth. It is well known that [GADV]-amino acids can be easily synthesized in Miller type experiments. [GADV]-proteins were produced, for example, by repeated heat-drying processes of [GADV]-amino acids in tide pools on the primitive Earth, and were further accumulated by pseudo-replication to form [GADV]-protein world. Subsequently, nucleotides and oligonucleotides were synthesized by their high catalytic activities in the world. The accumulation of oligonucleotides triggered the generation of GNC primeval genetic code through stereospecific complex formation among four [GADV]-amino acids and four corresponding GNC-containing oligonucletoides.
More efficient synthesis of [GADV]-proteins with the complexes than direct synthesis among individual [GADV]-amino acids assisted establishing the GNC primeval genetic code generation. Next, GNC-repeating sequences were produced by random phosphodiester bond formation on chiral [GADV]-proteins or by linear arrangement of GNC codons in the complexes of GNC-containing oligonucleotides and [GADV]-amino acids.
Thus, the first single-stranded (GNC)n gene was created, when one (GNC)n sequence encoding a [GADV]-protein with the required function was selected from a pool of (GNC)n polynucleotides, leading to the emergence of the first life. How the “chicken and egg relationship” between genes and proteins was formed on the primitive Earth also can be explained from the standpoint of GADV hypothesis as going up from the lower ([GADV]-protein synthesis) to the upper stream (creation of genes) of the genetic flow. In the RNA world hypothesis, it seems difficult to find a reasonable strategy for creation of the first gene. The notion of GNC primeval genetic code gave a motivation for introduction of the new concept or pseudo-replication of [GADV]-proteins.
Genetic information in the form of DNA base sequences or codon sequences is transformed into mRNA and then into amino acid sequence of proteins, according to the genetic code. But, double-stranded DNA, which carries genetic information, cannot be replicated without enzyme proteins, whereas proteins cannot be reproduced without genes. This dilemma made it difficult to account for the origin of life: this is the so-called chicken and egg relationship between genes and proteins in the life system.
The RNA world hypothesis on the origin of life is generally considered as the key to solve the “chicken and egg dilemma” concerning the evolution of genes and proteins as observed in the modern organisms. This hypothesis, however, contains several serious weak points, as followings. (i) Nucleotides would never be synthesized under pre-biotic conditions through a random combinatory process from simple chemical compounds such as water, carbon dioxide, methane, without proteineous enzymes. (ii) Existence of four hydroxyl groups on ribose also makes it difficult to synthesize RNA by joining nucleotides in the absence of enzyme catalysts. (iii) Self-replication of RNA must be practically impossible due to the following self-contradiction. RNA without any stable tertiary structure would be required to exhibit genetic function as a template, and, simultaneously, RNA would have to be folded into a stable tertiary structure to exhibit its catalytic function.
I have a counterproposal called [GADV]-protein world hypothesis, abbreviated as GADV hypothesis, in which I have suggested that life originated from a [GADV]-protein world, which comprised proteins composed of four amino acids: Gly [G], Ala [A], Asp [D], and Val [V]. A new concept “pseudo-replication” is crucial for the description of the emergence of life. The new hypothesis not only plausibly explains how life originated from the initial chaotic protein world, but also how genes, the genetic code, and proteins were originated and co-evolved.