Significance of strand configuration in self-replicating RNA molecules

The kinetic theory of replication has been extended to include dual mechanisms for conversion of self-annealed single-strand RNA to double-strand molecules, which do not replicate. An analysis of experimental results established that the replicate-template annealing reaction during transcription significantly retarded replication in vitro among three RNA variants copied by Q beta replicase. Annealing between complementary RNA strands free in solution had far less significance. The finding that an RNA variant can be replicated in a multiple hairpin configuration, but not as its single, long hairpin conformer, the correlation between stability of strand secondary structure and replicative fitness, and a lack of homology in the internal sequence of RNA variants copied by Q beta replicase support the conclusion that template competence depends on strand configuration, independent of most of the underlying base sequence. Occurrence of self-annealed strands in the Q beta replicase system was attributed to its reliance on RNA-driven strand separation, in the absence of enzyme catalysed strand unwinding. A 'configuration before sequence' path to self-replication exhibited a substantially lower combinatorial barrier than standard sequence-dependent evolution. RNA-dependent RNA synthesis in the Q beta system thus displays features of an RNA World and, interestingly, they reveal a rapid path for evolution of the first self-replicating molecule on Earth.