FIG. 3.

Effect of mutations in the 5′UTR of HCV-1b on IRES activity. IRES activity was assessed by measuring the ratio of the levels of RLUC and FFLUC produced from transfected bicistronic plasmid constructs in vTF7-3-infected cells. The activity of the prototype HCV-1b sequence (1b) was taken as 100%. (A) The activities of six 5′UTRs containing single point mutations expressed relative to that of the prototypic HCV-1b sequence are shown. (B) Complementation of mutated 5′UTRs with the prototypic genotype 1b 5′UTR was attempted. Biscistronic constructs expressing mutated 5′UTRs were transfected alone (black bars) or cotransfected with pHCV1bS (hatched bars) or with pHCV1bCAT (white bars) DNA. IRES activity was assessed as described above. Mutant 5′UTRs are designated according to the position of the changed nucleotide.