Expression and functional activities of Rex-2 mutants. (A) Western blot analysis of Rex-2 protein expressed from 293T cells transiently transfected with Rex-2 cDNA plasmids. Proteins were detected using rabbit Rex-2-specific antisera. wt p24 and p26 are indicated, and arrows identify truncated Rex proteins. α, anti. (B) Functional activities of Rex-2 cDNA mutants were determined using the modified HIV p24 Gag reporter assay. 293T cells were transfected with 0.25 μg pcTat, 0.5 μg pcGagRxRE-II, 0.05 μg CMV-Luc, and increasing concentrations of wt Rex or mutant Rex plasmids as indicated (0.02 to 0.5 μg). Forty-eight hours after transfection, cells were harvested and assayed for p24 Gag. The values represent actual p24 Gag production from a representative experiment performed in triplicate. Error bars indicate standard deviations.