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J. Virol., May 1995, 3017-3023, Vol 69, No. 5
L Yu, PM Loewenstein, Z Zhang and M Green
We have reported the molecular cloning, expression, and characterization of
a human cellular protein, TAP, which possesses a strong transcriptional
activation domain and binds the human immunodeficiency virus type 1 Tat
transactivator in vitro and in vivo (L. Yu, Z. Zhang, P.M. Loewenstein, K.
Desai, Q. Tang, D. Mao, J.S. Symington, and M. Green, J. Virol.
69:3007-3016, 1995). Here we show that TAP binds the general transcription
factor TFIIB. Furthermore, we delineate the binding domains of TAP, Tat,
and TFIIB, as well as measure the strengths and specificity of these
protein-protein interactions. TAP binds strongly to Tat, with a Kd of
(approximately 2 to 5) x 10(-7) M. The Tat activation region contains a
17-amino-acid conserved core domain which is the single contact site for
TAP. Single- amino-acid substitutions within the Tat core domain inactivate
transactivation in vivo and in vitro and greatly reduce binding of Tat to
TAP in vitro. TAP binds strongly to TFIIB, with about the same Kd as for
Tat. The interaction between TAP and TFIIB requires a sequence near the
carboxy terminus of TFIIB which is also required for binding the strong
acidic activator VP16. The contact sites for Tat and TFIIB map within the
TAP C-terminal region, which contains the TAP activation domain. These
combined results are consistent with the hypothesis that TAP is a cellular
coactivator that bridges the Tat transactivator to the general
transcription machinery via TFIIB.
Copyright © 1995, American Society for Microbiology
In vitro interaction of the human immunodeficiency virus type 1 Tat transactivator and the general transcription factor TFIIB with the cellular protein TAP
Institute for Molecular Virology, Saint Louis University School of Medicine, Missouri 63110, USA.
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