FIG. 2.

Transcriptional repression of the HIV-1 promoter by the US3 repressive element. The parental reporter gene construct, pEQ235, was drawn to scale. Open rectangle, HIV-1 sequences; gray rectangle, lacZ gene; thin line, multiple cloning region; X, XbaI site; H, HindIII site. US3 sequences were inserted into pEQ235 by using oligonucleotides with XbaI and HindIII ends and containing the depicted US3 sequences. The names of the resulting plasmids are listed. Plasmids were transfected into human diploid fibroblasts and subsequently mock infected (open rectangles) or infected with HCMV (cross-hatched rectangles). β-Galactosidase activity was measured as described in the legend to Fig. 1. The experiment was repeated a minimum of five times; the data presented are averages of duplicate experiments. Background levels of enzyme activity obtained with the promoterless control plasmid were subtracted from the test values.