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Open AccessConcept Paper

Universal Codons with Enrichment from GC to AU Nucleotide Composition Reveal a Chronological Assignment from Early to Late Along with LUCA Formation

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Roumen Tsanev Institute of Molecular Biology, Bulgarian Academy of Sciences, Acad. G. Bonchev Str. 21, Sofia 1113, Bulgaria
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Department of Molecular & Cellular Biology, Roswell Park Cancer Institute, Buffalo, NY 14263, USA
*
Author to whom correspondence should be addressed.
Life 2020, 10(6), 81; https://doi.org/10.3390/life10060081
Received: 3 May 2020 / Revised: 30 May 2020 / Accepted: 3 June 2020 / Published: 5 June 2020
(This article belongs to the Section Origin of Life)
The emergence of a primitive genetic code should be considered the most essential event during the origin of life. Almost a complete set of codons (as we know them) should have been established relatively early during the evolution of the last universal common ancestor (LUCA) from which all known organisms descended. Many hypotheses have been proposed to explain the driving forces and chronology of the evolution of the genetic code; however, none is commonly accepted. In the current paper, we explore the features of the genetic code that, in our view, reflect the mechanism and the chronological order of the origin of the genetic code. Our hypothesis postulates that the primordial RNA was mostly GC-rich, and this bias was reflected in the order of amino acid codon assignment. If we arrange the codons and their corresponding amino acids from GC-rich to AU-rich, we find that: 1. The amino acids encoded by GC-rich codons (Ala, Gly, Arg, and Pro) are those that contribute the most to the interactions with RNA (if incorporated into short peptides). 2. This order correlates with the addition of novel functions necessary for the evolution from simple to longer folded peptides. 3. The overlay of aminoacyl-tRNA synthetases (aaRS) to the amino acid order produces a distinctive zonal distribution for class I and class II suggesting an interdependent origin. These correlations could be explained by the active role of the bridge peptide (BP), which we proposed earlier in the evolution of the genetic code. View Full-Text
Keywords: origin of life; Darwinian evolution; universal genetic code; LUCA; pre-LUCA; first codon; RNA–peptide world; aminoacyl-tRNA synthetases; aaRS; bridge peptide; GC-rich codons; first life; first organism origin of life; Darwinian evolution; universal genetic code; LUCA; pre-LUCA; first codon; RNA–peptide world; aminoacyl-tRNA synthetases; aaRS; bridge peptide; GC-rich codons; first life; first organism
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MDPI and ACS Style

Gospodinov, A.; Kunnev, D. Universal Codons with Enrichment from GC to AU Nucleotide Composition Reveal a Chronological Assignment from Early to Late Along with LUCA Formation. Life 2020, 10, 81.

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