The emergence of molecular machines as a prerequisite of the ancient RNA world evolution

The problem of the start of biological evolution in the ancient RNA world is considered. It is postulated that the appearance of catalytic RNAs — ribozymes — via spontaneous cis- and trans-rearrangements of polyribonucleotides in primordial Darwin ponds should not have been sufficient for the start of evolution, until a new class of functional RNA, namely energy-dependent molecular machines, arose. The proposed hypothesis is that the simplest and primary type of molecular machines could be nucleoside triphosphate-dependent RNA-based helicases, which were capable of unwinding the stable double-helical RNAs inevitably formed during RNA syntheses on complementary templates. Thereupon, unwinding RNA polymerases could appear as a result of association or fusion of helicases and polyribonucleotide-polymerizing ribozymes. The latter event provided the mechanism of RNA replication using the double-helical RNAs as a communal genofond (gene pool) of a Darwin pond, and thus initiated the fast evolution of the ancient RNA world.