Transcription factor binding to the CRE sites in the CCR5 downstream promoter. (A) Scheme depicting the CCR5 gene and the downstream promoter region (P1). Locations of the identified putative CRE sites in the downstream promoter regions are depicted above. Sites at which significant protein binding was detected are indicated by large arrows, whereas sites that did not generate protein binding are indicated by small arrows. Underneath, the downstream promoter-luciferase-reporter constructs are shown. (B) EMSA showing binding of complexes to the CRE sites in the CCR5 downstream promoter region (CRE-B1 through -B13) and a CRE consensus probe (cons) using nuclear extracts of U251 cells (top panels) and primary T lymphocytes (bottom panels). Protein/DNA complexes are formed with probe CRE-B1 through -B5, -B7, -B8, -B12, and -B13. (C) Using specific antibodies, the complexes binding to CCR5-CRE-B1, -B3, -B4, and -B7 were shown to contain both CREB-1 and ATF-1, whereas the complexes formed with CCR5-CRE-B2, and CRE-B13 contained only CREB-1. *Supershifted complexes. Shown are representatives of 2 independent experiments. Empty lanes were deleted from the images.