Deletion mutagenesis of the BVDV SD-1 5' UTR. Relative translation efficiency in BHK cells stably transfected with dicistronic expression plasmids carrying 5' and 3' deletions in the 5' UTR. The SEAP and luciferase values are normalized to specific mRNA levels. Domains depicted in Fig. 3 are indicated above the schematic representations of the expression plasmids.