Pre-initiation complexes of HIV (PICH) from PBMC and HeLa cells specifically recognize the intact HIV wt core promoter. EMSAs were performed as in Figure 2. (A) HeLa nuclear extracts were used in binding reactions that were challenged by the addition of a 200 fold molar excess of the indicated unlabelled promoter competitors (lane 2 to 6). Lane 1 contains no competitor (−). Lane 2 contains a scrambled non specific competitor. The upper panel shows complexes in the EMSA reaction. Pre-initiation complexes of HIV (PICHs) and a non-specific complex are indicated by arrows at the left. Quantifications of EMSA bands are displayed in the table in the lower panel, expressed as the percentage of reduction of each complex’s intensity upon competition. Complexes whose intensities are reduced by 50% or more by the addition of unlabelled competing oligonucleotides are highlighted in red. (B) As in A except that nuclear extracts from activated PBMC were used. (C) Quantification of EMSA band intensities from panel A is shown in graphic form. The intensity of the most abundant PICH in the control lane (panel A lane 1) has been set to 100%. Red color is used to highlight reduction of 50% or more for each complex relative to its level in the control lane (−). Shades of grey are used to distinguish each PICH. Relative band intensity is given on the vertical Y-axis, complexes are indicated on the right (Z-axis), and competitor oligonucleotides on the left (X-axis). (D) As in C, except that the graph represents the relative band intensities of the EMSAs from panel B.