A functional initiator element in the human beta-globin promoter.

Core promoters are defined by the presence of either a TATA box at approximately 30 base pairs upstream of the transcriptional start site (+1) and/or an initiator element centered around the +1 site. The prevalence, function, and significance of the various combinations of core promoter elements are as yet unclear. We describe here the identification and characterization of an initiator element in the TATA-containing human beta-globin promoter. Mutagenesis of the beta-globin initiator element at positions +2/+3 and +4/+5 abrogates transcription in a heterologous construct. Interestingly, we have found a beta-globin initiator binding activity in nuclear extracts whose presence or absence correlates with function of the beta-globin initiator. Accordingly, this binding activity may be part of the machinery required for beta-globin initiator-dependent transcription. Our analysis further describes a previously uncharacterized beta-thalassemia mutation at the +1 site as a mutation that decreases beta-globin initiator activity. Finally, consistent with other initiator elements, the beta-globin initiator requires a TFIID-containing fraction for in vitro activity. Thus, the human beta-globin promoter contains an initiator element whose function, as revealed by a beta-thalassemia mutation, is of physiological relevance.