Figure 6.

Synergy between different activation domains and HIV-1 Tat. (a) HeLa cells were transfected with pGal₅-HIV2 CAT, pCMVβgal, and different Gal4 fusion activation domains with or without pSV-HIV-1 Tat. CAT activities were normalized by the spectrophotometrically determined β-galactosidase activity. The relative percent CAT conversions plus and minus pSV-HIV-1 Tat (from which the histograms were derived were as follows: SP1, 4.9 and 0.13; VP16, 10.0 and 3.2; CIITA, 10.9 and 6.0. The 36-fold activation observed in the presence of HIV-1 Tat is lower than the levels reported in the literature (50-fold approximately) (51). (b) Binding of [³⁵S]methionine-labeled p62 subunit of TFIIH to the activation domain of CIITA immobilized on glutathione beads. The experiments were performed as described in Figs. 3 and 5. The lanes represent ³⁵S labeled p62 alone (lane 1) or its interaction with GST and GST-CIITA (lanes 2 and 3, respectively). The background interaction between GST and p62 has been noted (51).