Identification of the c-fos promoter region required for Tat transactivation. (A) Schematic map of the c-fos promoter structure. (B) The 5′ endpoints of the deletion mutants are indicated. (C) Jurkat cells were cotransfected with the indicated c-fos promoter/CAT constructs plus tat/S or tat/AS. CAT activity is expressed as folds of activation with respect to cell lines transfected with FC3 alone. Data are reported as means ± SDs of four independent transfection experiments performed in duplicate.