Extensive interactions between HIV TAT and TAF(II)250

The HIV transactivator, Tat, has been shown to be capable of potent repress ion of transcription initiation. Repression is mediated by the C-terminal s egment of Tat, which binds the TFIID component, TAF(II)250, although the si te(s) of interaction were not defined previously. We now report that the in teraction between Tat and TAFII250 is extensive and involves multiple conta cts between the Tat protein and TAFII250. The C-terminal domain of Tat, whi ch is necessary for repression of transcription initiation, binds to a segm ent of TAFII250 that encompasses its acetyl transferase (AT) domain (885-10 34 amino acids (aa)). Surprisingly, the N-terminal segment of Tat, which co ntains its activation domains, also binds to TAF(II)250 and interacts with two discontinuous segments of TAFII250 located between 885 and 984 aa and 1 120 and 1279 aa. Binding of Tat to the 885-984 aa segment of TAFII250 requi res the cysteine-rich domain of Tat, but not the acidic or glutamine-rich d omains. Binding by the N-terminal domain of Tat to the 1120-1279 aa TAFII25 0 segment does not involve the acidic, cysteine- or glutamine-rich domains. Repression of transcription initiation by Tat requires functional TAFII250 . We now demonstrate that transcription of the HIV LTR does not depend on T AFII250 which may account for its resistance to Tat mediated repression. (C ) 2001 Elsevier Science B.V. All rights reserved.