Errors of the ancestral translation, LUCA, and nature of its direct descendants

Abstract

I analyzed the implications of the observation that the methyltransferases, Trm5 and TrmD, which perform the methylation of the 37th base (m1G37) in tRNAs of bacteria and archaea respectively, are not homologous proteins. The first implication is that these methyltransferases originated very late only when the fundamental lineages leading to bacteria and archaea had separated, otherwise the two methyltransferases would have been homologous enzymes, which they are not. The conclusion that Trm5 and TrmD originated only when the main lineages were defined would imply that at least some aspects of the translation, such as +1 frameshifting, were still in rapid and progressive evolution, that is, they were still originating. This would in itself imply a high rate of translation errors because the absence of m1G37 from tRNAs could have determined a high rate of +1 translational frameshifting in the reading of mRNAs, identifying this stage as that of a phase of the origin of the genetic code. Furthermore, the observation that the frameshifting mechanism was still in rapid and progressive evolution in such an advanced evolutionary stage would imply that other mechanisms concerning translation were still rapidly evolving simply because it would be very unique if only the frameshifting mechanism were the only one still originating. Importantly, the observation that in archaea m1G37 also acts as a determinant of the identity of the tRNACysGCA would imply in itself that some aspects of the origin of the genetic code were still originating, greatly strengthening the hypothesis that other aspects of the translation apparatus were still in rapid and progressive evolution. Then, all this would imply a status of progenote for LUCA and ancestors of archaea and bacteria because a high rate of translation errors would fall within the definition of progenote.