As a matter of course, the first gene must be formed in the absence of gene. On the other hand, many biopolymers including gene are produced under the genetic system in extant organisms. Thus far, no idea explaining how the first gene was formed in the absence of gene, has been proposed except the idea based on the GADV hypothesis. GADV means four amino acids; Gly [G], Ala [A], Asp [D] and Val [V]. In this article, a reliable answer to the question, how the first gene was generated, is provided. The idea is as follows. The first gene (genetic information) was formed by random joining of anticodons, GNCs, which were carried by primeval anticodon stem-loop (AntiC-SL) tRNAs produced during repeated cycles of random joining of nucleotides and degradation of oligonucleotides. However, it might be difficult for many persons to accept the idea, because tRNAs and metabolic pathways using various proteins, which are produced under genetic functions, must be used to form the first gene. Then, it is reconsidered based on definition of genetic information and minimum necessary things to generate the first gene in this article, how the first gene was generated. Consequently, it could be reconfirmed that five prototypes of members (genetic code, tRNA, metabolism, cell structure and protein) composing the fundamental life system, except gene, are certainly necessary to generate the first gene. Namely, it can be concluded that the first gene was formed through nucleotide metabolism with immature [GADV]-proteins, primeval AntiC-SL tRNA formation with immature [GADV]-proteins, formations of single-stranded (GNC)n codon sequence by random joining of anticodons, GNCs, carried by AntiC-SL tRNAs, double-stranded (ds)-(GNC)n RNA and maturation of an immature [GADV]-protein, which was produced from one strand of the ds-RNA. Thus, the first gene was formed using the five primitive or prototypes of members, which were produced in the absence of gene. There would be no other way for generating the first gene.

It has not been reasonably explained still now, how the “chicken and egg relationship” between gene and protein was formed, although RNA world hypothesis was proposed to aim at explaining formation process of the relationship about 40 years ago. On the other hand, GADV hypothesis advocates that life emerged after five members of the fundamental life system; cell structure, metabolism, tRNA, genetic code and gene, were piled up one by one onto immature [GADV]-proteins, which were produced by random joining of [GADV]-amino acids on the primitive Earth. Furthermore, formation process of the first (GNC)n RNA gene encoding a mature [GADV]-protein can be also reasonably explained according to the hypothesis as follows. Double-stranded (ds)-(GNC)n RNA could be produced by complementary strand synthesis of a single-stranded (ss)-(GNC)n RNA, which was formed by random joining of GNC anticodons carried by four types of AntiC-SL tRNAs. Successively, the first (GNC)n RNA gene was generated upon maturation of an immature [GADV]-protein, which was produced through expression of codon sequence on one strand of ds-(GNC)n RNA, as accumulating necessary base substitutions and raising a weak catalytic activity of the immature protein to a more active state. It is considered that, consequently, a gene encoding a mature protein, which has the “chicken and egg relationship”, was generated for the first time. Therefore, it can be concluded that the “chicken and egg relationship” was built not by formation of either one, gene or protein, but by maturation of an immature gene, which was lead by improvement of catalytic activity of an immature protein. That is, it can be concluded that the reason, why it was unable to give an answer to the question on the formation process of the “chicken-egg relationship” thus far, is because it was an unanswered question.

One of the problems, which make it difficult to solve the mystery of the origin of life, would be how life emerged in chemically complex messy environments on the primitive Earth. It is considered that three main points contributed to open the way to the emergence of life. (1) A characteristic inherent in [GADV]-amino acids, which are easily produced with prebiotic means. (2) Protein 0th-order structure or [GADV]-amino acid composition generating water-soluble globular protein with some flexibility, which can be produced even by random joining of [GADV]-amino acids. (3) Formation of versatile [GADV]-microspheres, which can grow, divide, proliferate even without genetic system, was the emergence of proto-life. (4) [GADV]-microspheres with a higher proliferation ability than others could be selected. The proto-Dawin evolution made it possible to proceed forward to creation of the core life system composed of (GNC)n gene, anticodon stem-loop tRNA or AntiC-SL tRNA (GNC genetic code) and [GADV]-protein. (5) Eventually, the first genuine life with the core life system emerged. Thus, the formation processes of [GADV]-protein and (GNC)n gene in chemically complex messy environments were the steps to the emergence of genuine life.

Proteins having a variety of functions play many essential roles in maintaining various life activities in organisms. Various methods, by which new protein functions can be artificially produced, have progressed rapidly upon development in recombinant DNA technology and effective screening techniques. However, the obtainable scope of the new functions has been restricted in a narrow range, because only functions of presently existing proteins can be used. On the other hand, it has been considered that it would be impossible to create an entirely new protein, which does not show any meaningful homology with any other amino acid sequences of previously existing proteins. The reason is because one amino acid sequence for a protein cannot be selected out from an extraordinary large amino acid sequence diversity as ~10130. As a matter of course, it is impossible to design an amino acid sequence of a protein in advance and a gene encoding the protein cannot be also formed through random process. Nevertheless, extant organisms have generated a variety of entirely new proteins in some way to make full use of them. This means that extant organisms have equipped a mechanism with which entirely new proteins can be produced under the present core life system composed of protein, tRNA (genetic code) and gene. In this article, first I introduce the mechanism, with which entirely new proteins are created in extant organisms, and further propose a novel strategy for application of the mechanism to protein engineering through creation of entirely new proteins, which could contribute to development of various industries.

Understanding the mechanism, how entirely new (EntNew) gene/protein or the first ancestral gene/protein of a family was created, should be one of the most important issues in the biological sciences. However, the mechanism is totally unknown still now. On the other hand, it is well known that mature protein is generally rigid and one catalytic center exists on the protein. Creation of such a mature EntNew gene/protein should be, of course, carried out through random process, because it cannot be designed in advance. However, the EntNew gene/protein never be created by random polymerization of the respective monomeric units, because of the extraordinary large sequence diversities of ~10¹⁸⁰ and ~10¹³⁰, respectively. Protein 0^th-order structure or a specific amino acid composition, in which immature but water-soluble protein can be produced even through random process, holds the key for solving the difficult problem. As it was fragmentally described in the previous papers how and where EntNew gene/protein was created, I describe in detail in this review three processes generating EntNew gene/protein with some flexibility under three genetic codes, the universal genetic code, SNS primitive code and GNC primeval code, and discuss why the mature gene/protein could be created through the processes.

The origin of life has not been solved as yet, in spit of the time passage more than thirty years from publication of RNA world hypothesis by W. Gilbert (1986), which is based on the “gene/replicator--first” theory. On the contrary, I have proposed [GADV]-protein world hypothesis (GADV hypothesis), assuming that life emerged from [GADV]-protein world, which is grounded on the “protein/metabolism-first” theory. However, two weak points of protein world hypothesis, (i) protein cannot be produced without gene, and (ii) protein cannot be self-replicated, have been frequently pointed out by supporters of RNA world hypothesis. Then, I examined whether the two weak points could be overcome by GADV hypothesis or not. From the results, it was confirmed that (i) [GADV]-protein could be pseudo-replicated in the absence of gene owing to protein 0^th-order structure or [GADV]-amino acids, and (ii) the replication ability is not always required from the beginning but it is sufficient to acquire it at some time point until the emergence of life. Thus, it was concluded that life emerged as [GADV]-protein world hypothesis, which is grounded on the “protein/metabolism-first” theory, expects.

All life on Earth uses three integrated molecular systems in which genetic information contained in DNA base sequences is transmitted to ribosomes by RNA and a genetic code, then translated into the amino acid sequences of structural and catalytic proteins. Therefore, the most important point for understanding the origin of life is to determine how such systems could emerge from random processes on the early Earth. In this review, two alternatives are compared: the RNA world hypothesis and the [GADV]-protein world hypothesis. [GADV] refers to four amino acids, Gly [G], Ala [A], Asp [D] and Val [V] that are conserved in the amino acid sequences of many common proteins. Here I will argue that the origins of the three primary processes required for life to begin can be better explained by the GADV hypothesis than the RNA world hypothesis. The GADV hypothesis also incorporates a conversion process by which random polymers can evolve into proteins with ordered sequences.