Ancient RNA World

Based on the modern concept of multiplicity of RNA functions, certain new mechanisms, which could have played a key role in the origin and evolution of the ancient RNA world, are discussed. In particular, the reaction of spontaneous transesterification of polyribonucleotides, which was discovered by A. B. Chetverin and colleagues, could result in elongation of short initial oligoribonucleotides and produce sequence variants for further natural selection of accidentally arising functionally active molecules. Further, the formation of mixed molecular colonies of RNA on moist solid media, such as clays, could have provided compartmentation of functional RNA ensembles in the absence of envelopes or membranes, which were necessary for further evolution of the RNA world. The systematic exponential enrichment of the RNA population with functionally the best molecules because of alternating dissolution of colonies due to flooding and formation of new colonies due to drying in ancient pools ("primordial natural SELEX") could be critical for the evolutionary process in the RNA world.