How ribosomal translation could have evolved remains an open question in most available scenarios for the early developments of life. Rather than considering RNA and peptides as two independent systems, this work is aimed at assessing the possibility of formation and stability of co-polymers or co-oligomers of α-amino acids and nucleotides from which translation might have evolved. Here we show that the linkages required to build such mixed structures have lifetimes of several weeks to months at neutral pH and 20 °C owing to the
mutual protecting effect
of both neighboring phosphoramidate and ester functional groups increasing their stability by factors of about 1 and 3 orders of magnitude, respectively. This protecting effect is reversible upon hydrolysis allowing the possibility of subsequent reactions. These copolymer models, for which an abiotic synthesis pathway is supported by experiments, form a basis from which both polymerization and translation could have logically evolved. Low temperatures were identified as a critical parameter for the kinetic stability of the aminoacylated nucleotide facilitating the synthesis of the model. This observation independently supports the views that any process involving RNA aminoacyl esters, outstandingly including the emergence of translation, was more probable at 0 °C or below and might be considered a kinetic marker constraining the environment in which translation has evolved.
Electronic supplementary material
The online version of this article (10.1007/s00239-019-9887-7) contains supplementary material, which is available to authorized users.
Nucleosides and methylated nucleotide models were used as substrates to identify pathways for the chemical aminoacylation of ribonucleic acids (RNA) as a prerequisite for the evolution of translation. A selective and comparatively efficient reaction of a 5(4H)-oxazolone with the 2′-and 3′-OH of the ribonucleotide models was observed. Surprisingly, a similar reaction starting from an α-amino acid N-carboxyanhydride (NCA), selected as an acylating agent potentially leading to the unprotected ester required for translation, was not observed, which was confirmed using an acylated NCA equivalent. The reasons for this difference are analysed.
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