Abstract
Recruitment of the P-TEFb kinase by HIV-1 Tat to the viral promoter triggers the phosphorylation and escape of RNA polymerase II from promoter-proximal pausing. It is unclear, however, if Tat recruits additional host factors that further stimulate HIV-1 transcription. Using a sequential affinity-purification scheme, we have identified human transcription factors/coactivators AFF4, ENL, AF9, and elongation factor ELL2 as components of the Tat-P-TEFb complex. Through the bridging functions of Tat and AFF4, P-TEFb and ELL2 combine to form a bifunctional elongation complex that greatly activates HIV-1 transcription. Without Tat, AFF4 can mediate the ELL2-P-TEFb interaction, albeit inefficiently. Tat overcomes this limitation by bringing more ELL2 to P-TEFb and stabilizing ELL2 in a process that requires active P-TEFb. The ability of Tat to enable two different classes of elongation factors to cooperate and coordinate their actions on the same polymerase enzyme explains why Tat is such a powerful activator of HIV-1 transcription.
Copyright (c) 2010 Elsevier Inc. All rights reserved.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Binding Sites
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Cell Line
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Cyclin-Dependent Kinase 9 / metabolism
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HIV-1 / genetics*
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HIV-1 / metabolism
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Host-Pathogen Interactions
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Humans
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Multiprotein Complexes
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Nuclear Proteins / metabolism
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Positive Transcriptional Elongation Factor B / metabolism
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Promoter Regions, Genetic
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Proteasome Endopeptidase Complex / metabolism
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Proteasome Inhibitors
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RNA Interference
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RNA, Viral / biosynthesis*
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Repressor Proteins / genetics
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Repressor Proteins / metabolism*
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Transcriptional Activation*
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Transcriptional Elongation Factors / metabolism
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Transfection
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tat Gene Products, Human Immunodeficiency Virus / genetics
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tat Gene Products, Human Immunodeficiency Virus / metabolism*
Substances
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AFF4 protein, human
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ELL protein, human
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ELL2 protein, human
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MLLT3 protein, human
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Multiprotein Complexes
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Nuclear Proteins
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Proteasome Inhibitors
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RNA, Viral
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Repressor Proteins
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Transcriptional Elongation Factors
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tat Gene Products, Human Immunodeficiency Virus
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Positive Transcriptional Elongation Factor B
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CDK9 protein, human
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Cyclin-Dependent Kinase 9
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Proteasome Endopeptidase Complex