[PDF][PDF] HIV-1 Tat and host AFF4 recruit two transcription elongation factors into a bifunctional complex for coordinated activation of HIV-1 transcription

N He, M Liu, J Hsu, Y Xue, S Chou, A Burlingame… - Molecular cell, 2010 - cell.com
N He, M Liu, J Hsu, Y Xue, S Chou, A Burlingame, NJ Krogan, T Alber, Q Zhou
Molecular cell, 2010cell.com
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 …
Summary
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.
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