Evolutionary origins of the RNA-guided nucleotide-modification complexes: from the primitive translation apparatus?

Eukarya and Archaea possess scores of RNA-guided nucleotide-modification complexes that target specific ribonucleotides for 20-O-methylation or pseudouridylation. Recent characterization of these RNA-modification machines has yielded striking results with implications for their evolutionary origins: the two main classes of nucleotide-modification complex in Archaea share a common ribonucleoprotein (RNP) core element that has evolved from a progenitor RNP. The fact that this common RNP element is also found in ribosomes suggests that the origin of the progenitor RNP lies in the primitive translation apparatus. Thus, the trans-acting, RNAguided nucleotide-modification complexes of the modern RNP world seem to have evolved from cis-acting RNA or RNP elements contained in the primitive translation apparatus during the transition from the ancient RNA world to the modern RNP world.