NF-κB-mediated activation of the human immunodeficiency virus enhancer: Site of transcriptional initiation is independent of the TATA box

The activation of the human immunodeficiency virus (HIV) enhancer in T cells can occur through multiple independent pathways. This enhancer is stimulated by NF-κB or through alternative mechanisms, including E1A transactivation, which is dependent on the TATA box. In this report, the role of the TATA box in activation by NF-κB is examined. E1A stimulation of the HIV enhancer requires the presence of the TATA sequence in the sense orientation. Analysis of mutant HIV enhancer plasmids shows that basal mRNA levels are reduced when the TATA sequence is altered but that inducibility of NF-κB and the site of transcriptional initiation are unchanged. These data suggest that transcriptional initiation in this class II promoter is determined by an initiator factor which does not require binding to the TATA sequence. Because κB is found in a variety of viruses, this mechanism may be relevant to the activation of other viral enhancers.