INTERACTION OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 TAT WITH A UNIQUE SITE OF TFIID INHIBITS NEGATIVE COFACTOR DR1 AND STABILIZES THE TFIID-TFIIA COMPLEX

We have previously reported the direct physical interaction between th e human immunodeficiency virus (HIV) type 1 Tat protein and the basal transcription factor TBP/TFIID. Affinity chromatography demonstrated t hat wild-type Tat, but not a transactivation mutant of Tat, was capabl e of depleting TBP/TFIID from cell extracts. These experiments represe nted the first demonstration of a basal transcription factor that bind s, in an activation-dependent manner, to Tat. We now report that the T at-TBP interaction can be detected in HIV type 1-infected cells. The d omain of TBP interacting with Tat has been mapped from amino acids 163 to 196 by using deletion and site-specific mutants of TBP. This domai n of TBP, which includes the H1 and S2 domains, is distinct from the H 2 binding site for other activator proteins, such as E1A. The interact ion of Tat with TFIID regulates the binding of accessory proteins to T FIID. Tat stabilizes the interaction of TFIID with TFIIA in a gel shif t assay. In addition, Tat competes for Drl interaction with TBP. bur r esults suggest that the basal transcription factor TBP/TFIID represent s an important regulatory molecule in HIV transcription.