Characterization of a transcriptional attenuator within the 5' R region of the human T cell leukemia virus type 1.

Several regulatory sequences have been characterized in the HTLV-I promoter. We report here identification of a sequence element downstream of the transcriptional start site within the first 52 nucleotides of the 5' R region, which acts negatively on the activity of the HTLV-I promoter. Determination of the half-lives of the RNAs either including or lacking this sequence element showed that the observed effect intervenes at the transcriptional level. This negative element does not affect basal activity of the HTLV-I TATA box, but down-regulates transcription induced by strong activators. Thus, we propose that this so-called negative regulatory sequence functions as an attenuator of transcription.