THE HIV-1 INDUCER OF SHORT TRANSCRIPTS ACTIVATES THE SYNTHESIS OF 5,6-DICHLORO-1-BETA-D-BENZIMIDAZOLE-RESISTANT SHORT TRANSCRIPTS IN-VITRO

The HIV-1 inducer of short transcripts (IST) is an unusual promoter el ement that activates the synthesis of short transcripts from the HIV-1 promoter as well as from heterologous promoters. While the DNA sequen ces constituting IST have been characterized in some detail, little is known about the biochemical mechanisms underlying IST activity. Here, we describe a cell-free transcription assay that faithfully reproduce s the synthesis of IST-dependent HIV-1 short transcripts. As in vivo, formation of these short transcripts requires a functional IST element and is repressed in the presence of the viral trans-activator Tat, Sh ort transcript and full-length transcript synthesis respond differentl y to variations in several reaction parameters, suggesting that the sh ort and full-length transcripts are synthesized by transcription compl exes with distinct biochemical properties, In particular, short transc ript synthesis is resistant to the action of 5,6-dichloro-1-beta-D-ben zimidazole, an inhibitor of transcript elongation. Formation of transc ription complexes directed by the IST element may, therefore, not requ ire the activity of a factor inhibited by 5,6-dichloro-1-beta-D-benzim idazole, such as the TFIIH-associated or pTEFb kinases.