Gene and promoter organization of human CC chemokine receptor CCR5. Schematic representation of the CCR5 gene and its promoters. Exons (1-3) are depicted by boxes. Both promoter regions, the downstream promoter P1 and the upstream promoter P2, are indicated above the scheme. Locations of the identified putative transcription factor binding sites are depicted above. Underneath, promoter-luciferase-reporter constructs used in this study are shown. Two sets of constructs were used: the upstream promoter constructs CCR5-pA1 through -pA4 and the downstream promoter constructs CCR5-pB1 and -pB3 through -pB5. Nucleotide positions for the exons and the promoter constructs are depicted relative to the ORF in exon 3. Numbering of nucleotides and exons is according to the CCR5 numbering system proposed at the 1999 CCR5-AIDS symposium.^26,34