Translation of SINV sgmRNAs bearing termination codons at different positions. (A) RNA secondary structure of 5′ UTRs predicted by RNAfold (see legend in Fig. 1A). (B) BHK (upper panel), PKR−/− MEFs (middle panel), and C6/36 (lower panel) cells were transfected with Lipofectamine 2000 and the corresponding SINV replicons transcribed in vitro. Seven, 5, and 8 h later, respectively, cells were harvested to measure luciferase activity. Values are plotted as means ± SD of three independent experiments. The percentage values obtained from mutant replicons relative to control rep C+luc are shown in the graph. SINV C accumulation was analyzed in parallel by Western blotting with a specific anti-C antibody. (C) The amounts of genuine protein C were quantified by densitometric scanning of the corresponding autoradiographs. Values are represented as means ± SD of three representative experiments. Numbers above the bars indicate the percentage values obtained from rep C+luc STOP and rep C+luc hSTOPp relative to rep C+luc AUG-hp. (D) Synthesis of sgmRNA in BHK cells transfected with the different SINV replicons and processed as indicated in Figure 2D,F.