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Molecular and Cellular Biology, April 1999, p. 2863-2871, Vol. 19, No. 4
Department of Molecular and Cell Biology,
University of California at Berkeley, Berkeley, California 94720
Received 11 September 1998/Returned for modification 13 October
1998/Accepted 15 December 1998
Tat stimulates human immunodeficiency virus type 1 (HIV-1)
transcriptional elongation by recruitment of the human transcription elongation factor P-TEFb, consisting of Cdk9 and cyclin T1, to the
HIV-1 promoter via cooperative binding to the nascent HIV-1 transactivation response RNA element. The Cdk9 kinase activity has been
shown to be essential for P-TEFb to hyperphosphorylate the
carboxy-terminal domain (CTD) of RNA polymerase II and mediate Tat
transactivation. Recent reports have shown that Tat can also interact
with the multisubunit transcription factor TFIIH complex and increase
the phosphorylation of CTD by the Cdk-activating kinase (CAK) complex
associated with the core TFIIH. These observations have led to the
proposal that TFIIH and P-TEFb may act sequentially and in a concerted
manner to promote phosphorylation of CTD and increase polymerase
processivity. Here, we show that under conditions in which a specific
and efficient interaction between Tat and P-TEFb is observed, only a
weak interaction between Tat and TFIIH that is independent of critical
amino acid residues in the Tat transactivation domain can be detected.
Furthermore, immunodepletion of CAK under high-salt conditions, which
allow CAK to be dissociated from core-TFIIH, has no effect on either
basal HIV-1 transcription or Tat activation of polymerase elongation in
vitro. Therefore, unlike the P-TEFb kinase activity that is essential
for Tat activation of HIV-1 transcriptional elongation, the CAK kinase
associated with TFIIH appears to be dispensable for Tat function.
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Tat Activates Human Immunodeficiency Virus Type 1 Transcriptional
Elongation Independent of TFIIH Kinase
*
Corresponding author. Mailing address: 206 Stanley
Hall, #3206, University of California, Berkeley, Berkeley, CA 94720. Phone: (510) 643-1697. Fax: (510) 643-9290. E-mail:
qzhou{at}uclink4.berkeley.edu.
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