Two RNA Worlds: Toward the Origin of Replication, Genes, Recombination, and Repair

Abstract

All modern organisms depend on genomes that encode a diversity of RNA molecules functioning in a plethora of physiological, regulatory, and fundamental functions. Processes like gene transcription into mRNA, ribozyme catalyzed translation in the heart of ribosomes, RNA interference (RNAi), reverse transcription and defense of transposons, retroelements, homing mobility of introns, and many other characteristics of life represent the smoking gun of primordial RNA based, complementary base pairing driven search processes crucial for the origin of life and all successive life. This chapter overviews the necessary steps of RNA dependent evolutionary processes that lead to the emergence of replication, genes, recombination, and repair. The top to bottom journey into the past starts with the concept of Popper’s deductive cycle. It leads us through established knowledge accompanied by the conserved mechanism of homology search engines as a key feature of the modern RNA world to the structure based ribozyme function of the catalytic center of the peptidyltransferase in modern ribosomes. We then jump over to the ancient RNA world in a bottom to top approach, a tactic taken by other chapters in this book as well. We use theoretical evidence for a ~55 nt protoribosome as the endpoint of this bottom to top journey and join again with the current RNA world by pointing out the statistical detection of an ancient RNY code in modern genes.