A downstream element in the human β-globin promoter: Evidence of extended sequence-specific transcription factor IID contacts

We describe here the identification and characterization of a functional downstream element in the human adult β-globin promoter. The existence of this element was indicated by two mutations at +22 and +33 downstream of the β-globin transcriptional start site in humans with β-thalassemia. In vitro transcriptional analysis of these mutants, plus a third at +13, indicates that all three decrease transcription from the β-globin promoter. Scanning mutagenesis from +10 to +45 indicates that this region contains a functional cis element(s) in vitro, and we designated this element the DCE (downstream core element). The DCE functions in concert with the β-globin CATA box and initiator element, as well as in a heterologous, TATA-less context. A second set of mutants indicates that a particular geometry of the DCE and core promoter is necessary for promoter function. Lastly, DCE mutants show reduced affinity for transcription factor lid (TFIID). These data indicate that TFIID makes sequence-specific contacts to the DCE and that TFIID binding is necessary for DCE function.