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The bromodomain protein Brd4 is a positive regulatory component of P-TEFb and stimulates RNA polymerase II-dependent transcription.

Brd4 is a mammalian bromodomain protein that binds to acetylated chromatin. Proteomic analysis revealed that Brd4 interacts with cyclinT1 and Cdk9 that constitutes core positive transcription elongation factor b (P-TEFb). Brd4 interacted with P-TEFb in the living nucleus through its bromodomain. About half of P-TEFb was bound to the inhibitory subunit and functionally inactive. Brd4 interacted with P-TEFb that was free of the inhibitory subunit. An increase in Brd4 expression led to increased P-TEFb-dependent phosphorylation of RNA polymerase II (RNAPII) CTD and stimulation of transcription from promoters in vivo. Conversely, a reduction in Brd4 expression by siRNA reduced CTD phosphorylation and transcription, revealing that Brd4 is a positive regulatory component of P-TEFb. In chromatin immunoprecipitation (ChIP) assays, the recruitment of P-TEFb to a promoter was dependent on Brd4 and was enhanced by an increase in chromatin acetylation. Together, P-TEFb alternately interacts with Brd4 and the inhibitory subunit to maintain functional equilibrium in the cell.

Pubmed ID: 16109376


  • Jang MK
  • Mochizuki K
  • Zhou M
  • Jeong HS
  • Brady JN
  • Ozato K


Molecular cell

Publication Data

August 19, 2005

Associated Grants


Mesh Terms

  • Animals
  • Cyclin-Dependent Kinase 9
  • DNA, Complementary
  • Mice
  • Nuclear Proteins
  • Oncogene Proteins, Fusion
  • Positive Transcriptional Elongation Factor B
  • Promoter Regions, Genetic
  • RNA Polymerase II
  • RNA, Small Nuclear
  • Transcription Factors
  • Transcription, Genetic