Novel internal promoter/enhancer of HTLV-I for Tax expression.

The transcription initiation signals in retroviruses lie within the long terminal repeat (LTR) sequences. We have found a new transcriptional promoter in a central portion of the genome of human T-cell leukaemia virus type I (HTLV-I). The transcription start site is located just upstream to the ATG codon of the transcriptional trans-activator molecule, tax protein (Tax). The internal promoter may provide a new insight into gene expression of HTLV-I. The mechanism of leukaemogenesis by the defective HTLV-I is also discussed. Furthermore, we have identified two repeats of a novel enhancer sequence AGTTCT, which are located around the initiation site. We call the sequence HIRE (HTLV-I Internal Regulatory Element).