FIG. 1.

Poliovirus CRE and RNA replicons. (A) Wild-type (WT) CRE structure and mutations engineered into the CRE structure. The CRE presented is based on the enterhino CRE common motif proposed by Yang et al. (50) . (B) Mutant CRE RNA structure. (C and D) Diagrams of RNA replicons possessing either wild-type CRE or mutant CREs. (C) Replicons used to assay positive-strand RNA synthesis. Replicons with 5′-terminal hammerhead ribozymes were used to generate replicon RNAs with authentic 5′ termini necessary for positive-strand RNA synthesis. (D) Replicons used to assay negative-strand RNA synthesis. Replicons with two 5′-terminal guanosine residues (capable of inhibiting positive-strand RNA synthesis) were used to characterize negative-strand RNA synthesis that is independent of positive-strand RNA synthesis.