Cis-element, oriR, involved in the initiation of (-) strand poliovirus RNA: a quasi-globular multi-domain RNA structure maintained by tertiary ('kissing') interactions.

The key steps in the replication of the poliovirus genome, initiation of (-) and (+) strands, require two different cis-acting elements, oriR and oriL, respectively. It has been proposed that the spatial organization of these elements is maintained by tertiary ('kissing') interactions between the loops of two constituent hairpins. Here, the putative partners of the kissing interaction within the oriR of the full-length poliovirus RNA were modified by site-directed mutagenesis. The destabilization of this interaction resulted in a severe suppression of the viral RNA synthesis, but the mutant transcripts proved to be infectious. With a single exception, the potential for the kissing interaction within the oriR of the recovered viruses was partially or completely restored due to either true reversions or second-site compensatory mutations. There was a good correlation between the restoration of this potential and the phenotypic properties of the viruses. It was concluded that the kissing interaction in the poliovirus oriR is functionally important. Using the above experimental data, a three-dimensional structure was derived by molecular modeling techniques, which demonstrated the overall feasibility of the proposed interactions and displayed the poliovirus oriR as a quasi-globular multi-domain structure.