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PubMed2025

Crick's "Frozen accident theory" of the genetic code explored by Ising models.

Francis Crick proposed that the almost universal genetic code could be nothing more than a 'frozen accident'. The Ising model, widely used in statistical mechanics, is used to explore patterns which could achieve a phase transition mimicking the frozen accident. Codons are considered as nodes and amino acids as spins. Monte Carlo simulations of the 64-node genetic code models are carried out. Anti-ferromagnetic interactions or a combination of ferro and anti-ferromagnetic interactions can lead to stable, regular patterns resembling the genetic code. It is indeed found that the 64-node Ising system exhibits critical slowing down dynamics, compatible with a freezing process. These models aim to simulate the formation of patterns similar to the genetic code through physical freezing processes, providing insights into potential mechanisms and processes that may have contributed to the formation and evolution of the genetic code.

Genetic Code↗

PubMed2026

Alternative genetic codes in bacteria and archaea identified with a fast k-mer-based algorithm.

The genetic code is conserved across all domains of life and is often described as universal. Nevertheless, many exceptions to the "universal" code have now been documented, most of these through manual or semiautomated inspection of highly conserved genes. Modern bioinformatics tools improved our ability to find alternative genetic codes but remain computationally expensive, preventing widespread use on thousands of new species identified by sequencing environmental samples. Here, I report a >100-fold accelerated method for inferring the genetic code directly from assembled genomes and apply it to thousands of previously uncharacterized assemblies from archaea and bacteria. I describe three candidate genetic code variations, one of which, an alternative genetic code used by a family of Asgard archaea, is a unique example of sense codon reassignments for this domain. Identifying genetic code variations is important for understanding evolution of the standard code and improving accuracy of protein databases and open reading frame identification.

Genetic Code↗

PubMed1992

A statistical test of hypotheses on the organization and origin of the genetic code.

Theories of the origin of the genetic code assign different weights to amino acid properties such as polarity and precursor-product relationship. Previous statistical work on the origin of the genetic code has produced controversial results. We analyze relationships between various amino acid and tRNA properties by one and the same statistical method. It is shown that polarities as well as precursor-product relationships are both likely to have been important in shaping the genetic code, together with codon swapping that left protein sequences intact.

Amino Acids↗

PubMed1986

Laws governing degeneration of the genetic code.

The laws governing degeneration of the genetic code are discussed below. Of fundamental importance in this context is the classification of the amino acids into groups on the basis of the physicochemical behaviour of their residues. From this, it is possible to formulate arithmetic relationships between the number of amino acids in the same group and the number of coding triplets. It is found that the degeneration of the genetic code obeys certain laws, the reasons for this being related to the number and the qualitative properties of the amino acids and triplets. The fact that the three bases of a coding triplet have different priorities must also be a critical factor.

Amino Acid Sequence↗

PubMed1988

The degeneracy rule of genetic code.

The degeneracy rules of genetic code including the distribution of terminators have been deduced through the minimization of mutational deterioration (MD). The MD of a given group of codons is divided into three parts: transitional, transversional and wobble's. The averaged mutational deteriorations (AMD) of various amino acids have been proved in order of their degrees of irreplaceability.

Amino Acids↗

PubMed2026

The proteomic origin of the genetic code.

INTRODUCTION: The origin and evolution of the genetic code is a central problem in molecular biology. Classical models have emphasized stereochemistry, frozen accidents, or adaptive optimization, often treating proteins as passive products of preexisting codes. More recent views instead portray the code as a dynamic, coevolving system shaped by reciprocal interactions among amino acids, RNA, and early catalysts. AREAS COVERED: Here, I review efforts of phylogeny reconstruction of the history of tRNA, protein structural domains, and dipeptide sequences in proteomes. These complementary approaches allow exploration of the entry of amino acids and codons into the code, and the transition from an operational RNA code in the tRNA acceptor arm to the canonical code in the anticodon loop. Evidence for ancestral synthetase enzymes with dual functions in aminoacylation and peptide-bond formation, as well as early bidirectional (sense-antisense) coding reflected in dipeptide-antidipeptide emergence is also discussed. EXPERT OPINION: The genetic code is best viewed as a proteome-driven, evolvable system in which early peptides actively shaped coding rules by stabilizing structure, expanding chemical diversity, and enhancing catalysis. This perspective connects origin-of-life studies with modern efforts of code expansion, translational engineering, and peptide-based therapeutics, highlighting the impact of the code's proteomic origin.

Genetic Code↗

PubMed2026

The genetic code at the balance point of error and demand.

The origin and organizing principles of the genetic code remain central problems in molecular evolution. The low probability of the natural codon-to-amino acid mapping arising by chance has spurred the hypothesis that its structure is optimized for robustness to mutations and translational errors. For the construction of effective molecular machines, the repertoire of encoded amino acids must also be diverse enough in physicochemical features. Here, we examine whether the standard genetic code can be understood as a near-optimal solution balancing these two objectives: minimizing error load and aligning codon assignments with the naturally occurring amino acid composition. Using simulated annealing, we explore this trade-off across a broad range of parameters. We find that the standard genetic code resides near an optimum in the fitness landscape of possible genetic codes. The degeneracy of the code plays a dual role, minimizing mistranslation errors while matching codon multiplicity to amino acid usage frequencies. As a result, uniform codon usage alone is sufficient to recover the empirical amino acid composition, without any additional bias. It is a highly effective solution that balances fidelity against resource availability constraints. A comparative analysis of natural variants also reveals a functional decoupling: error robustness acts as a rigid global constraint determined by code topology, whereas compositional alignment serves as a more flexible variable that adapts to lineage-specific demands. These results support a multi-objective optimization framework in which the genetic code reflects a balance between translational fidelity and proteomic demand.

Genetic Code↗

PubMed1978

The genetic code as a periodic table.

The contemporary genetic code is reflective of a significant correlation between the properties of amino acids and their anticodons in a periodic manner. Almost all properties of amino acids showed a greater correlation to anticondonic than to codonic dinucleoside monophosphate properties. The polarity and bulkiness of amino acid side chains can be used to predict the anticodon with considerable confidence. The results are most consistent with predictions of the "direct interaction" and "ambiguity reduction" hypotheses for the origin of the genetic code.

Amino Acids↗

PubMed1986

Deviations from the 'universal' genetic code.

Experimental data show that ciliates and mycoplasmas have genetic codes different from the 'universal' code. An evolutionary scheme which could explain the origin of terminators in a genetic code and relate it to the phenomenon of nuclear dimorphism in ciliates is proposed.

Amino Acid Sequence↗

PubMed1987

Evolution of anticodons: variations in the genetic code.

Clues to evolution of the genetic code can be found by comparing usage of anticodons in various organisms and organelles. GC content of DNA varies, as a result of directional mutation pressure (AT/GC pressure), especially in bacteria. Low GC in Mycoplasma is accompanied by use of UGA for tryptophan and, in ciliated protozoa, by use of UAA and UAG for glutamine. These are examples of "stop codon capture," which has been preceded by duplication of tRNA genes followed by nucleotide substitutions in their sequences, including mutational changes in their anticodons. Evolutionary changes in the code may have resulted from disappearance of codons and anticodons resulting from GC pressure and from their reappearance when the direction of the pressure was reversed. In this manner, codon UGA and anticodon UCA for tryptophan could have disappeared under GC pressure and reappeared in Mycoplasma under AT pressure. Stop codon UGA may have been the third of the three stop codons to appear, originating from mutations in UAA. Changes in the code are adaptive and nondeleterious. We propose that the number of anticodons has increased and that evolution continued until three existing forms of the universal code were produced: eukaryotic, eubacterial, and the code for halobacteria and methanococci. These three codes are distinguished from each other by their anticodon pattern. The eukaryotic code contains eight INN (ANN) anticodons that have replaced GNN anticodons as a result of AT pressure. Mitochondrial and chloroplast codes have evolved from the eubacterial code through genomic economization and AT pressure, leading to losses of GNN and CNN anticodons.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acids↗

PubMed1990

The revised genetic code.

Recent findings on the genetic code are reviewed, including selenocysteine usage, deviations in the assignments of sense and nonsense codons, RNA editing, natural ribosomal frameshifts and non-orthodox codon-anticodon pairings. A multi-stage codon reading process is presented.

Genetic Code↗

PubMed1976

A cybernetic approach to the origin of the genetic coding mechanism. II. Formation of the code series.

The sequential fulfillment of the principle of succession necessarily guides the main steps of the genetic code evolution to be reflected in its structure. The general scheme of the code series formation is proposed basing on the idea of "group coding" (Woese, 1970). The genetic code supposedly evolved by means of successive divergence of pra-ARS's loci, accompanied by increasing specification of recognition capacity of amino acids and triplets. The sense of codons had not been changed on any step of stochastic code evolution. The formulated rules for code series formation produce a code version, similar to the contemporary one. Based on these rules the scheme of pra-ARS's divergence is proposed resulting in the grouping of amino acids by their polarity and size. Later steps in the evolution of the genetic code were probably based on more detailed features of the amino acids (for example, on their functional similarities like their interchangeabilities in isofunctional proteins).

Amino Acids↗

PubMed1990

Is genetic code redundancy related to retention of structural information in both DNA strands?

We have noted that the sense-antisense relationships inherent in the genetic code divide the amino acids into three separate groups. The nature of the amino acids in each group may allow the polypeptides coded by the antisense strand to retain the secondary structure patterns of the translated strand. Also, this relationship requires all but eight of the codons in the eukaryotic code and all but four in the mitochondrial code. Thus, genetic code redundancy could be related to evolutionary pressure toward retention of protein structural information in both strands of DNA.

Amino Acids↗

PubMed1976

The genetic code and the origin of life.

The problem of the origin of life understandably counts as one of the most exciting questions in the natural sciences, but in spite of almost endless speculation on this subject, it is still far from its final solution. The complexity of the functional correlation between recent nucleic acids and proteins can e.g. give rise to the assumption that the genetic code (and life) could not originate on the Earth. It was Portelli (1975) who published the hypothesis that the genetic code could not originate during the history of the Earth. In his opinion the recent genetic code represents the informational message transmitted by living systems of the previous cycle of the Universe. Here however, we defend the existence of a certain strategy in the syntheses of the genetic code during the history of the Earth. The strategy of correlation between amino acid and nucleotide polymers made an increasing velocity of the chemical evolution possible, that is, it increased the velocity of formation of the genetic code. Thus, life with the recent genetic code could originate on the Earth within the present cycle of the Universe.

Amino Acids↗

PubMedDate not supplied

On the relationships between the genetic code coevolution hypothesis and the physicochemical hypothesis.

This paper analyzes the relationships between the genetic code coevolution hypothesis and the physicochemical hypothesis by means of a comparative study of the precursor-product amino acid pairs on which the former hypothesis is based. Even if the coevolution between the biosynthetic relationships of amino acids and the organization of the genetic code is not questioned in this paper, the results and the arguments used lead us to believe that the selective pressures considered essential by the physicochemical postulates, played a more active role than that of the precursor-product relationships in defining the allocation of these amino acids in the genetic code. It is furthermore pointed out that the two evolutionary hypothesis might be aspects of the same selective pressure, and thus difficult to differentiate.

Amino Acids↗

PubMedDate not supplied

[Physico-chemical basis of the genetic code origin: stereochemical analysis of interactions of amino acids and nucleotides based on the progene hypothesis].

A progene hypothesis has been proposed earlier to explain the mechanism of origin of the self-reproducing genetic system. Progenes (precursors of the genetic system) are mixed anhydrides of an amino acid and deoxyribotrinucleotide at the 3'-gamma-terminal phosphate (NpNpNppp-AA); they are produced from dinucleotides (NpNp) and 3'-gamma-aminoacylnucleotidylates (Nppp-AA) as a result of specific interaction between amino acid and dinucleotide. The postulated mechanism of progene formation accounts for the selection of substances, including chirality, the origin of the genetic code as well as for the mechanisms of formation, self-reproduction and evolution of the simpliest genetic system ("gene--polypeptide"). A stereochemical analysis of the progene formation mechanism has allowed us to support the main statements of the hypothesis that relate to the origin of the genetic code and to selection of substances. Atomic groups that could be responsible for the specificity of interaction between dinucleotides and amino acids in progene formation have been revealed. Stereochemical evidence for the physicochemical basis of the origin of the existing genetic code have been produced: 1) a special role of the second nucleotide in the codon is demonstrated in amino acid coding by the progene hypothesis principle; 2) an advantage of T against U in such coding is demonstrated; 3) for 16 amino acids out of 20 an agreement has been obtained between the optimal dinucleotide as revealed by the stereochemical analysis and the codon dinucleotides; 4) an explanation for the third nucleotide selection mechanism is offered. A restoration of the prebiotic code, based on these results, has indicated that the code contains 32 codons, is statistical and group-wise. It encodes 7 groups of isofunctional amino acids: 3 overlapping groups of non-polar amino acids 1) medium-size hydrophobic amino acids (chiefly Val, n-Val and a-But), 2) small and medium-size non-polar amino acids (chiefly Ala Val, n-Val a-But and Gly), 3) small non-polar amino acids (Gly, Ala, a-But) and 4 groups of polar amino acids--1) hydroxy--+dicarbonic (Asp, Glu, Ser and Thr), 2) dicarbonic (Asp and Glu), 3) hydroxy (Ser and Thr) and 4) basic (Arg and Lys). The code includes about 20 amino acids among which are 15-17 canonical and a few common non-canonical. The prebiotic code explains many properties of the existing genetic code and is capable of evolving into the latter by way of a gradual replacement of the physicochemical coding mechanism by the enzymatic coding mechanism.

Amino Acids↗

PubMed1989

On the information content of the genetic code.

In living organisms 20 amino acids along with the terminator value(s) are encoded by 64 codons giving a degeneracy of the codons as described by the genetic code. A basic theoretical problem of genetic codes is to explain the particular distribution of degeneracies of partitions involved in the codes. In this work the degeneracy problem is considered in the framework of information theory. It is shown by direct numerical evaluation of a certain degeneracy information function associated with the genetic code that the degeneracy of the codes is observed to be related to the optimization of this function.

Amino Acids↗

PubMed1989

Optimization and the genetic code.

The present paper will focus on the relation between the structure of the table of the genetic code and the evolution of primitive organisms: it will be shown that the organization of the code table according to an optimization principle based on the notion of resistance to errors can provide a criterium for selection. The ordered aspect of the genetic code table makes this result a plausible starting point for studies of the origin and evolution of the genetic code: these could include, besides a more refined optimization principle at the logical level, some effects more directly related to the physico-chemical context, and the construction of realistic models incorporating both aspects.

Biological Evolution↗