FIG. 6.

Efficient expression of Tat from the native tat mRNA in astrocytes. The fluorescence of cells expressing GFP was measured by flow cytometry of HeLa cells (A) or U251MG cells (C) that were transfected with 5 μg of pLTR-EGFP together with increasing amounts of pNL4-3 (0.05, 0.2, 2.0, 10.0, or 20.0 μg [lanes 1, 3, 5, 7, and 9, respectively]) or pNL4-3Tat− (0.05, 0.2, 2.0, 10.0, or 20.0 μg [lanes 2, 4, 6, 8, and 10, respectively]). Transfections included 2 μg of pCMV-hGH to control for transfection efficiency. Fluorescence (see Materials and Methods) was expressed as the ratio of basal fluorescence obtained from transfections of pLTR-EGFP without Tat and normalized for hGH production. Shown are mean values and standard errors of the means of data from four experiments. Soluble p24 antigen was measured in HeLa (B) or U251MG (D) culture supernatant samples collected prior to cell harvesting and normalized for hGH production.