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Replication and gene expression of the human immunodeficiency virus (HIV) requires the trans-activator protein, Tat. The Tat protein provides the first example of a viral protein that regulates transcriptional elongation in eukaryotic cells. A major theme is the use of cell-free transcription systems to study the mechanism of action of Tat and its cellular co-factors. The results demonstrate that Tat is first recruited to the HIV promoter by binding to the TAR RNA leader sequence, then activates specific protein kinase, called TAK (Tat-associated kinase). Current work aims at understanding how phosphorylation by TAK permits activated transcriptional elongation. A second theme we are exploring is how integrated and latent HIV proviruses respond to cellular signaling pathways. Recently we have discovered that the transcription factor NF-kB is able to stimulate both elongation and initiation. We are currently studying the role of NF-kB in HIV transcription using a combination of technologies involving the use of retroviral vector to establish models for latently infected cells and chromatin immunoprecipitation assays to study transcription. In a complementary study, we are examining the role of Notch signaling factors CBF-1 in mediating changes in chromatin structure during the establishment of HIV latency.
Selected Publications
Kim YK, Bourgeois CF, Pearson R, Tyagi M, West MJ, Wong J, Wu SY, Chiang CM, Karn J: Recruitment of TFIIH to the HIV LTR is a rate-limiting step in the emergence of HIV from latency. EMBO J. 2006 Aug 9;25(15):3596-604. [PubMed]
Murchie AIH, Davis B, Afshar M, Drysdale MJ, Bower J, Potter AJ, Starkey ID, Swarbrick TM, Isel C, Lentzen G, Prescott CD, Aboul-ela F, Karn J (2004) Structure-Based Drug Design Targeting an Inactive RNA Conformation: Exploiting the Flexibility of HIV-1 TAR RNA. J. Mol. Biol., 336, 625-638. [PubMed]
Davis B, Afshar M, Varani G, Murchie AIH, Karn J, Lentzen G, Drysdale M, Bower J, Potter AJ, Starkey ID, Swarbrick T, Aboul-ela F (2004) Rational Design of Inhibitors of HIV-1 TAR RNA through the Stabilization of Electrostatic "Hot Spots". J. Mol. Biol., 336, 343-356. [PubMed]
Kim Y-K, Bourgeois C, Isel C & Karn J,(2002) Phosphorylation of the RNA polymerase CTD promotes read-through of terminator sequences. Mol. Cell Biol., 22, 4622-4637. [PubMed]
Bourgeois C, Kim Y-K, Churcher MJ, West MJ & Karn J,(2002) Spt5 cooperates with Tat by preventing premature RNA release at terminator sequences. Mol. Cell. Biol., 22, 1079-1093. [PubMed]
West MJ, Lowe AD & Karn J (2001) Activation of HIV transcription in T-cells revisited: NF-kB p65 stimulates transcriptional elongation. J. Virol. 75, 8524-8537. [PubMed]
Isel C & Karn J (1999) Direct evidence that human immunodeficiency virus type-1 Tat activates the Tat-associated kinase (TAK) during transcription elongation. J. Mol. Biol., 290, 929-941. [PubMed]
West MJ & Karn J (1999) Stimulation of Tat-associated kinase-independent transcriptional elongation from the human immunodeficiency virus type-1 long terminal repeat by a cellular enhancer. EMBO J., 18, 1378-1386. [PubMed]
Najera I, Krieg M & Karn J (1999) Synergistic stimulation of HIV-1 Rev-dependent export of unspliced mRNA to the cytoplasm by HnRNP A1. J. Mol. Biol., 285, 1951-1964. [PubMed]
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