The evolution of proteome: From the primeval to the very dawn of LUCA.

The attempt to delineate the essential features that characterized life in its beginnings and the understanding of how those features evolved, represent important scientific challenges. While there have been varied efforts in the elucidation of how the first biomolecules arose from a prebiotic environment, there remains important gaps towards the characterization of the complete repertoire of the Last Universal Common Ancestor (LUCA). We portray a step-wise proteome evolution, by looking at the phenotype encoded by each one of the genetic codes that were appearing along evolution, beginning with the primeval genetic code and then with two intermediate Extended RNA codes, which finally shaped the current Standard Genetic Code (SGC). Notably, all molecules involved in translation, such as ribosomal proteins and all tRNA synthetases, were already present before LUCA. The metabolism belonged to extremophiles as hinted by the presence of reverse gyrase and acetyl coenzyme A synthase. Furthermore, we predict the structure and possible ligands of the proteins retrieved. We have forged a bridge between the hitherto unknown proteome of progenotes and the proteome of LUCA.