[Tax, the puppet master of HTLV-1 transcription]

Retroviruses exploit the RNA polymerase II transcription machinery for the transcription of their genes. This is the case of Human T-lymphotropic virus type 1 (HTLV-1), the retrovirus responsible for adult T-cell leukemia and for various inflammatory diseases. HTLV-1 transcription is under the control of the viral protein Tax, which exhibits an original mode of action since it does not rely on direct promoter interaction but rather on the recruitment of various cellular factors and cofactors of transcription. The factors that Tax recruits are involved in the initial step of promoter activation but also in the subsequent steps of the transcription process itself. This review describes this particular mechanism of viral transcription, from the epigenetic release of the viral promoter to the elongation of the neosynthesized viral silencing transcripts.