THE ROLE OF RNA STRUCTURE IN RNA REPLICATION

RNA replication by RNA replicas has two puzzling features: (i) its selectivity, i.e. only a few RNA species can be replicated, (ii) strand separation, i.e., a single-stranded RNA template is used to produce a complementary replica; both template and replica are liberated as single-stranded RNA. Sequence comparison of a great number of replicating RNA species did not reveal sequence homologies except for the invariant ends. However, a structural element required for the replication has been identified: 5' termini were found to be involved in intramolecular base-pairing while the 3' termini were not. Artificially designed short RNA sequences having this structural property were synthesized and found to replicate. The results suggest that the RNA structures of template and replica participate directly in catalyzing the replication, in particular in the separation of strands during RNA replication.