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J. Virol., 05 1995, 3007-3016, Vol 69, No. 5
L Yu, Z Zhang, PM Loewenstein, K Desai, Q Tang, D Mao, JS Symington and M Green
The mechanism by which human immunodeficiency virus type 1 Tat
transactivates the long terminal repeat promoter is not understood. It is
generally believed that Tat has one or more transcription factors as its
cellular target. One might expect a cellular target for Tat to possess
several properties, including (i) the ability to bind to the Tat activation
region, (ii) the possession of a transcriptional activation domain, and
(iii) the ability to contact the cellular transcription machinery. Here we
describe the cloning, expression, and characterization of a human protein,
termed TAP (Tat-associated protein), which possesses some of these
properties. TAP is highly conserved in eukaryotes and is expressed in a
variety of human tissues. The major intracellular species of TAP is a
highly acidic 209-amino- acid protein that likely is formed by removal of a
highly basic 70- amino-acid N-terminal segment from a primary translation
product. By deletion analysis, we have identified a TAP C-terminal region
rich in acidic amino acids and leucine residues which acts as a strong
transcriptional activator when bound through GAL4 sites upstream of the
core long terminal repeat promoter, as well as flanking sequences that mask
the activation function. Amino acid substitution of two leucine residues
within the core activation region results in loss of the TAP activation
function. Two lines of evidence suggest that Tat interacts with TAP in
vivo. First, promoter-bound Tat can recruit a TAP/VP16 fusion protein to
the promoter. Second, transiently expressed Tat is found associated with
endogenous TAP, as demonstrated by coimmuno- precipitation analysis. As
shown in an accompanying report, the TAP activation region binds the Tat
core activation region and general transcription factor TFIIB (L. Yu, P.M.
Loewenstein, Z. Zhang, and M. Green, J. Virol. 69:3017-3023, 1995). These
combined results suggest the hypothesis that TAP may function as a
coactivator that bridges Tat to the general transcription machinery of the
cell via TFIIB.
Copyright © 1995, American Society for Microbiology
Molecular cloning and characterization of a cellular protein that interacts with the human immunodeficiency virus type 1 Tat transactivator and encodes a strong transcriptional activation domain
Institute for Molecular Virology, Saint Louis University School of Medicine, Missouri 63110, USA.
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