FIG. 4.

Cell-based HIV-1 frameshifting assay. (A) Schematic representation of the RNA constructs used in the cell-based frameshifting assay. The constructs were designed along similar lines as the in vitro constructs. In the FSP construct, functional SEAP (4) is produced only when frameshifting occurs. The S17 construct contains a modified HIV-1 frameshift signal so that when translated it produces the same protein as the FSP construct but without the requirement for frameshifting. (B) RG501 stimulates frameshifting in cells. COS cells were transfected with either FSP (▪) or S17 (□) expression vectors. After incubation in the presence of RG501 (final DMSO concentration, 0.5%) for 48 h, SEAP levels were determined with a chemiluminescence SEAP kit (Tropix). The RLUs for each concentration of RG501 were normalized to those from cells incubated in medium supplemented with 0.5% DMSO.