BIOCHEMICAL AND GENETIC-EVIDENCE FOR A PSEUDOKNOT STRUCTURE AT THE 3'TERMINUS OF THE POLIOVIRUS RNA GENOME AND ITS ROLE IN VIRAL-RNA AMPLIFICATION

The sequences in the plus-stranded poliovirus RNA genome that dictate the specific amplification of viral RNA in infected cells remain unkno wn. We have analyzed the structure of the 3' noncoding region of the v iral genome by thermodynamic-based structure calculation and by chemic al and enzymatic probing of in vitro-synthesized RNAs and provide evid ence for the existence of an RNA pseudoknot structure in this region. To explore the functional significance of this structure, revertants o f a mutant bearing a lesion in the proposed pseudoknot and exhibiting a temperature-sensitive defect in viral RNA synthesis were isolated an d mapped. The results of this genetic analysis established a correlati on between the structure of the 3' terminus of the viral RNA and its f unction in vivo in RNA amplification. Furthermore, phylogenetic analys is indicated that a similar structure could be formed in coxsackieviru s B1, a related enterovirus, which further supports a role for the pse udoknot structure in viral RNA amplification in infected cells.