Boreskov

PL‐7CONVEYING RNA‐BASED MOLECULAR MACHINES AS A PREREQUISITETO THE ORIGIN AND EVOLUTION OF THE ANCIENT RNA WORDSpirin A.S. and Chetverin A.B.Institute of Protein Research, Russian Academy of Sciences,Pushchino, Moscow Region, Russia 142290The appearance of catalytic RNA molecules (ribozymes) capable of synthesizingoligoribonucleotides and polyribonucleotides is supposed to be a key event in the origin ofthe ancient RNA world. By now the synthetic ribozymes with template‐directed RNApolymerizingactivity have been created under laboratory conditions. However, as theproducts of these ribozymes are complementary to their templates, they inevitably collapseinto the form of very stable RNA double helices incapable of acquiring catalytic activities(conformational paradox [1]). The emergence of ribozyme‐based molecular machines of theconveying type capable of unwinding secondary structures of polynucleotides is postulatedhere as a revolutionary occasion that allowed the RNA world to evolve towards the livingworld.The main principle of molecular nanomachines is the use of the Brownian motion as adriving force for the movement of the machine, instead of the use of mechanical powerstrokes in macromachines. The unidirectionality of the movement is provided by energydependent“pawls” (back stops) that allow molecular machines to move ahead and impedebackward moves (rectification of random motions). In the present‐day biological world, RNAand DNA polymerases, translating ribosomes and the systems of intracellular transport (suchas actin/myosin and kinesin/tubulin systems) are the best studied examples of suchmolecular machines of the conveying type. All of them, except ribosomes, are built ofproteins, whereas the ribosome is an RNA‐based nanomachine [2]. Being a processiveribozyme, the ribosome is capable of energy‐dependent unidirectional moving along apolyribonucleotide chain as a template (conveying machine function) and simultaneouslysynthesizing polypeptide chain from amino acids (peptide polymerase function). It isimportant that during its movement along the template polyribonucleotide, the ribosomeunwinds the secondary structure of the template chain (RNA helicase function).We hypothesize that the first RNA‐based conveying machine of the ancient RNA worldwas an RNA‐polymerizing ribozyme with coupled helicase (“unwindase”) activity. It could be16