FIG. 1.

5′-UTR of poliovirus type 1. The IRES includes the predicted secondary-structure domains II to VI, the oligopyrimidine tract (py), and the silent AUG in domain VI. The authentic polyprotein start codon is at position 743. In this study, the single nucleotide exchanges that contribute to the attenuation of neurovirulence of the respective poliovirus Sabin vaccine strains were generated artificially in the domain V (blow-up) of the otherwise unchanged poliovirus type 1 IRES sequence. In these constructs (named S1, S2, and S3, respectively), the luciferase sequence is fused directly to the poliovirus initiator AUG at position 743.