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Phosphorylated positive transcription elongation factor b (P-TEFb) is tagged for inhibition through association with 7SK snRNA.

The positive transcription elongation factor b (P-TEFb), comprising CDK9 and cyclin T, stimulates transcription of cellular and viral genes by phosphorylating RNA polymerase II. A major portion of nuclear P-TEFb is sequestered and inactivated by the coordinated actions of the 7SK snRNA and the HEXIM1 protein, whose induced dissociation from P-TEFb is crucial for stress-induced transcription and pathogenesis of cardiac hypertrophy. The 7SK.P-TEFb interaction, which can occur independently of HEXIM1 and does not by itself inhibit P-TEFb, recruits HEXIM1 for P-TEFb inactivation. To study the control of this interaction, we established an in vitro system that reconstituted the specific interaction of P-TEFb with 7SK but not other snRNAs. Using this system, together with an in vivo binding assay, we show that the phosphorylation of CDK9, on possibly the conserved Thr-186 in the T-loop, was crucial for the 7SK.P-TEFb interaction. This phosphorylation was not caused by CDK9 autophosphorylation or the general CDK-activating kinase CAK, but rather by a novel HeLa nuclear kinase. Furthermore, the stress-induced disruption of the 7SK.P-TEFb interaction was not caused by any prohibitive changes in 7SK but by the dephosphorylation of P-TEFb, leading to the loss of the key phosphorylation important for 7SK binding. Thus, the phosphorylated P-TEFb is tagged for inhibition through association with 7SK. We discuss the implications of this mechanism in controlling P-TEFb activity during normal and stress-induced transcription.

Pubmed ID: 14627702


  • Chen R
  • Yang Z
  • Zhou Q


The Journal of biological chemistry

Publication Data

February 6, 2004

Associated Grants

  • Agency: NIAID NIH HHS, Id: AI-41757

Mesh Terms

  • Cyclin T
  • Cyclin-Dependent Kinase 9
  • Cyclins
  • HeLa Cells
  • Humans
  • In Vitro Techniques
  • Mutation
  • Phosphorylation
  • Positive Transcriptional Elongation Factor B
  • Protein Binding
  • RNA Interference
  • RNA, Small Nuclear
  • RNA-Binding Proteins
  • Recombinant Proteins
  • Transcription, Genetic