C-JUN, C-FOS AND THEIR FAMILY MEMBERS ACTIVATE THE TRANSCRIPTION MEDIATED BY 3 21-BP REPETITIVE SEQUENCES IN THE HTLV-I LONG TERMINAL REPEAT

Transcription of human T-cell leukemia virus type I is regulated by a viral transactivatior Tax, through the 21-bp sequence in the long term inal repeat (LTR). We found that cellular transcription factor AP-1 (c -Jun/c-Fos hetero-complex) bound to the 21-bp sequence. The binding af finity of the complex increased in proportion to the number of the 21- bp sequence, and the transcriptional activation by AP-1 became evident only when the reporters had more than three 21-bp sequences. Thus, AP -1 may play a role in the viral transcription from the LTR with three 21-bp sequences in the absence of Tax, such as in the early stage of t he virus infection.