Cross-talk between orientation-dependent recognition determinants of a complex control RNA element, the enterovirus oriR

The coxsackie B3 virus oriR is an element of viral RNA thought to promote the assembly of a ribonucleoprotein complex involved in the initiation of genome replication. The mutual orientation of its two helical domains X and Y is determined by a kissing interaction between the loops of these domains. Here, a genetic approach was worked out to identify spatial orientation-dependent recognition signals in these helices. Spatial orientation changes (due to linear and rotational shifts) were introduced by appropriate insertions/deletions of a single base pair into one or both of the domains, and phenotypic consequences caused by these mutations were studied. The insertion of a base pair into domain Y caused a defect in viral reproduction that could be suppressed by a base-pair insertion into domain X. Similarly, a defect in viral replication caused by a base-pair deletion from domain X could be suppressed by a base-pair deletion from domain Y. Thus, certain areas of the two domains should cross-talk to one another in the sense that a change of space position of one of them required an adequate reply (change of space position) from the other. Phenotypic effects of the local rotation of one or more base pairs (and of some other mutations) in either domain X or domain Y suggested that the two most distal base pairs of these domains served as orientation-dependent recognizable signals. The results were also consistent with the notion that the recognition of the distal base pair of domain Y involved a mechanism similar to the intercalation of an amino acid residue.