CDK-9/cyclin T (P-TEFb) is required in two postinitiation pathways for transcription in the C. elegans embryo

Genes Dev. 2002 Aug 15;16(16):2135-46. doi: 10.1101/gad.999002.


The metazoan transcription elongation factor P-TEFb (CDK-9/cyclin T) is essential for HIV transcription, and is recruited by some cellular activators. P-TEFb promotes elongation in vitro by overcoming pausing that requires the SPT-4/SPT-5 complex, but considerable evidence indicates that SPT-4/SPT-5 facilitates elongation in vivo. Here we used RNA interference to investigate P-TEFb functions in vivo, in the Caenorhabditis elegans embryo. We found that P-TEFb is broadly essential for expression of early embryonic genes. P-TEFb is required for phosphorylation of Ser 2 of the RNA Polymerase II C-terminal domain (CTD) repeat, but not for most CTD Ser 5 phosphorylation, supporting the model that P-TEFb phosphorylates CTD Ser 2 during elongation. Remarkably, although heat shock genes are cdk-9-dependent, they can be activated when spt-4 and spt-5 expression is inhibited along with cdk-9. This observation suggests that SPT-4/SPT-5 has an inhibitory function in vivo, and that mutually opposing influences of P-TEFb and SPT-4/SPT-5 may combine to facilitate elongation, or insure fidelity of mRNA production. Other genes are not expressed when cdk-9, spt-4, and spt-5 are inhibited simultaneously, suggesting that these genes require P-TEFb in an additional mechanism, and that they and heat shock genes are regulated through different P-TEFb-dependent elongation pathways.

Publication types

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

MeSH terms

  • Animals
  • Caenorhabditis elegans / embryology*
  • Caenorhabditis elegans Proteins*
  • Cyclin-Dependent Kinase 9
  • Cyclin-Dependent Kinases / metabolism*
  • Gene Expression Regulation, Developmental
  • Microscopy, Fluorescence
  • Models, Biological
  • Models, Genetic
  • Nuclear Proteins / metabolism
  • Phenotype
  • Phosphorylation
  • Positive Transcriptional Elongation Factor B
  • Protein-Serine-Threonine Kinases / metabolism*
  • Protein-Serine-Threonine Kinases / physiology*
  • RNA / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Saccharomyces cerevisiae Proteins / metabolism
  • Transcription Factors / metabolism
  • Transcription, Genetic*
  • Transcriptional Elongation Factors*


  • Caenorhabditis elegans Proteins
  • DSIF protein, C elegans
  • Nuclear Proteins
  • SPT4 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Transcription Factors
  • Transcriptional Elongation Factors
  • RNA
  • Positive Transcriptional Elongation Factor B
  • Protein-Serine-Threonine Kinases
  • Cyclin-Dependent Kinase 9
  • Cyclin-Dependent Kinases
  • cdk9 protein kinase, C elegans