Stability of replicative form and fitness among RNA variants transcribed by Qbeta replicase.

Abstract

Stability in the replicative form of RNA molecules transcribed by Qbeta replicase was demonstrated to provide a sequence-dependent indicator of their fitness. This follows from the finding that replication rates reported for 17 RNA species (genome length, 77-370 nucleotides) correlate with the self-interaction free energy of these self-annealed strands. Formation of double-stranded molecules during replication conversely decreased with self-interaction free energy. H-bond formation between self-complementary segments of folded RNA molecules plainly produces a potential energy barrier opposing the transition to a double-stranded, non-replicating form. Melting point temperature and resistance of RNA synthesis to elevated salt levels among three variants also increased with strand configuration free energy. Genome-based estimates of fitness in other self-replicating RNA species were therefore possible. Once a link between the kinetic parameters of replication and base sequence of these RNA species is adequately established, estimates of fitness can be dissociated from survival states following evolution, and Darwin's fundamental precept, 'survival of the fittest,' could be appraised as an experimentally testable hypothesis.