FIG. 6.

Effect of the 60-bp FR-α cDNA element on RSV-Luc expression in various cell lines. In RSV-Luc, the RSV promoter is upstream of the luciferase reporter gene. In construct 1, the 60-bp FR-α cDNA fragment (nt 234 to 293 relative to the transcription start site) is placed in the 5′ UTR of the reporter in RSV-Luc. Construct 2 is similar to construct 1 except that the 60-bp insert corresponds to the homologous FR-β cDNA sequence. Luciferase activity was measured in cells transfected with RSV-Luc, construct 1, or construct 2. Cells were transfected with 0.5 μg of the plasmid and harvested 48 h later to measure luciferase activity. The data represent ratios to the corresponding values for RSV-Luc. Uniformity in transfection efficiency was ensured in a parallel experiment in which plasmid DNA was purified from the transfected cells at the time of the harvest, digested with HindIII and XbaI, subjected to Southern blot analysis, and probed with ³²P-labeled luciferase cDNA (results not shown).