MUTATIONS IN THE CARBOXY-TERMINAL DOMAIN OF TBP AFFECT THE SYNTHESIS OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 FULL-LENGTH AND SHORT TRANSCRIPTS SIMILARLY

The human immunodeficiency virus type 1 promoter generates two types o f RNA molecules, full-length transcripts and short transcripts. Synthe sis of the short transcripts depends on the inducer of short transcrip ts (IST), an element located downstream of the start site. In the pres ence of the viral activator Tat, the synthesis of full-length transcri pts is up-regulated while that of short transcripts is down-regulated. Full-length and short transcripts, are probably generated by differen t types of transcription complexes. The first is IST independent, capa ble of efficient elongation, and up-regulated by Tat. The second is IS T dependent, incapable of efficient elongation, and down-regulated by Tat. We have used an in vivo assay to assess the role of TBP in human immunodeficiency virus type 1 transcription and to test the effect of mutations in TBP on synthesis of full-length and short transcripts. We find that TBP bound to the TATA box is required for the synthesis of short and full-length transcripts as well as for Tat activation and th at both yeast TBP and the carboxy-terminal domain of human TBP can rep lace full-length human TBP for these processes. Mutations in TBP affec t the synthesis of short and full-length transcripts as well as Tat ac tivation similarly, and these effects correlate with the previously de scribed effects of these mutations on binding of TBP to the TBP-associ ated factor TAF(II)250 in vitro. Together, these results suggest that if short and full-length transcripts are generated by variant transcri ption complexes, these complexes use TBP similarly, probably as part o f the TFIID complex.