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

Mol Cell. 2010 May 14;38(3):428-38. doi: 10.1016/j.molcel.2010.04.013.

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.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Binding Sites
  • Cell Line
  • Cyclin-Dependent Kinase 9 / metabolism
  • HIV-1 / genetics*
  • HIV-1 / metabolism
  • Host-Pathogen Interactions
  • Humans
  • Multiprotein Complexes
  • Nuclear Proteins / metabolism
  • Positive Transcriptional Elongation Factor B / metabolism
  • Promoter Regions, Genetic
  • Proteasome Endopeptidase Complex / metabolism
  • Proteasome Inhibitors
  • RNA Interference
  • RNA, Viral / biosynthesis*
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Transcriptional Activation*
  • Transcriptional Elongation Factors / metabolism
  • Transfection
  • tat Gene Products, Human Immunodeficiency Virus / genetics
  • tat Gene Products, Human Immunodeficiency Virus / metabolism*

Substances

  • AFF4 protein, human
  • ELL protein, human
  • ELL2 protein, human
  • MLLT3 protein, human
  • Multiprotein Complexes
  • Nuclear Proteins
  • Proteasome Inhibitors
  • RNA, Viral
  • Repressor Proteins
  • Transcriptional Elongation Factors
  • tat Gene Products, Human Immunodeficiency Virus
  • Positive Transcriptional Elongation Factor B
  • CDK9 protein, human
  • Cyclin-Dependent Kinase 9
  • Proteasome Endopeptidase Complex