Post-transcriptional modifications play major roles in the structure and function of transfer RNA. Inosine 34 is one of the few essential tRNA modifications, and its distribution among phyla and among tRNAs is highly asymmetrical. In extant eukaryotes the essential nature of I34-containing tRNAs is easily explained by the absence of isoacceptors with G-ended anticodons, which make the former the only means to decode C-ended codons. However, this does not explain why I34 was initially adopted by eukaryotic species at the root of the evolution of nucleated cells.

To understand the selective pressures that drove the significant enrichment in I34-containing tRNAs in eukaryotes we analyzed thousands of bacterial and eukaryotic genomes, and have experimentally studied the distribution of I34 among these species. We will present evidence that support that ADAT evolved and was universally selected in eukaryotes because its activity allows these cells to more efficiently synthesize a specific type of highly repetitive and low-complexity proteins. We will show that the human proteome contains families of proteins that are extremely enriched in amino acids that are potentially translated by ADAT-modified tRNAs. As the composition in these amino acids increases, the codon usage in human genes is increasingly biased towards triplets recognized by ADAT-modified tRNAs. Interestingly, many of these protein families are unique to eukaryotes. I will posit that the proteins whose synthesis is improved by ADAT may have played a part in the evolution of fundamental eukaryotic characters.

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CV of Lluis Ribas