Requirement for a kinase-specific chaperone pathway in the production of a Cdk9/cyclin T1 heterodimer responsible for P-TEFb-mediated tat stimulation of HIV-1 transcription

J Biol Chem. 2000 Jan 7;275(1):279-87. doi: 10.1074/jbc.275.1.279.


Tat activation of HIV-1 transcription is mediated by human transcription elongation factor P-TEFb, which interacts with Tat and phosphorylates the C-terminal domain of RNA polymerase II. The catalytic subunit of the P-TEFb complex, Cdk9, has been shown to interact with cyclin T and several other proteins of unknown identity. Consequently, the exact subunit composition of active P-TEFb has not been determined. Here we report the affinity purification and identification of the Cdk9-associated proteins. In addition to forming a heterodimer with cyclin T1, Cdk9 interacted with the molecular chaperone Hsp70 or a kinase-specific chaperone complex, Hsp90/Cdc37, to form two separate chaperone-Cdk9 complexes. Although the Cdk9/cyclin T1 dimer was exceptionally stable and produced slowly in the cell, free and unprotected Cdk9 appeared to be degraded rapidly. Several lines of evidence indicate the heterodimer of Cdk9/cyclin T1 to be the mature, active form of P-TEFb responsible for phosphorylation of the C-terminal domain of RNA polymerase II interaction with the Tat activation domain, and mediation of Tat activation of HIV-1 transcription. Pharmacological inactivation of Hsp90/Cdc37 function by geldanamycin revealed an essential role for the chaperone-Cdk9 complexes in generation of Cdk9/cyclin T1. Our data suggest a previously unrecognized chaperone-dependent pathway involving the sequential actions of Hsp70 and Hsp90/Cdc37 in the stabilization/folding of Cdk9 as well as the assembly of an active Cdk9/cyclin T1 complex responsible for P-TEFb-mediated Tat transactivation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Benzoquinones
  • Cell Cycle Proteins / metabolism
  • Chaperonins
  • Cyclin T
  • Cyclin-Dependent Kinase 9
  • Cyclin-Dependent Kinases / metabolism
  • Cyclins / metabolism*
  • DNA Polymerase II / metabolism
  • Dimerization
  • Drosophila Proteins*
  • Enzyme Activation
  • Gene Products, tat / metabolism*
  • HIV-1 / genetics*
  • HSP70 Heat-Shock Proteins / metabolism
  • HSP90 Heat-Shock Proteins / metabolism
  • Humans
  • Lactams, Macrocyclic
  • Molecular Chaperones / metabolism*
  • Positive Transcriptional Elongation Factor B
  • Protein Binding / drug effects
  • Protein Serine-Threonine Kinases / metabolism*
  • Quinones / pharmacology
  • Species Specificity
  • Transcription, Genetic
  • tat Gene Products, Human Immunodeficiency Virus


  • Benzoquinones
  • CCNT1 protein, human
  • CDC37 protein, human
  • Cell Cycle Proteins
  • CycT protein, Drosophila
  • Cyclin T
  • Cyclins
  • Drosophila Proteins
  • Gene Products, tat
  • HSP70 Heat-Shock Proteins
  • HSP90 Heat-Shock Proteins
  • Lactams, Macrocyclic
  • Molecular Chaperones
  • Quinones
  • tat Gene Products, Human Immunodeficiency Virus
  • Positive Transcriptional Elongation Factor B
  • Protein Serine-Threonine Kinases
  • CDK9 protein, human
  • Cyclin-Dependent Kinase 9
  • Cyclin-Dependent Kinases
  • DNA Polymerase II
  • Chaperonins
  • geldanamycin