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A kinase subunit of the human mediator complex, CDK8, positively regulates transcriptional activation

Tadashi Furumoto1, Aki Tanaka, Mitsuhiro Ito

  • 1Graduate School of Frontier Biosciences, Osaka Universuty, Suita, Osaka 565-0871, Japan.

Genes to Cells : Devoted to Molecular & Cellular Mechanisms
|January 11, 2007
PubMed

Insights

Researchers investigated the structure and function of human TRAP/Mediator complexes. They found distinct complexes, including CDK8-containing ones, that regulate transcription and RNA polymerase II phosphorylation, with CDK8 playing a positive role in activation.

Area of Science:

  • Molecular Biology
  • Gene Regulation
  • Protein Complexes

Background:

  • The Mediator complex, including TRAP/Mediator subunits, is crucial for regulating gene transcription.
  • Understanding the structural and functional diversity of Mediator subcomplexes is essential for deciphering gene expression control.

Purpose of the Study:

  • To characterize the structural and functional properties of human TRAP/Mediator complexes containing MED6, MED7, and CDK8.
  • To investigate the roles of these complexes in transcriptional regulation and RNA polymerase II modification.

Main Methods:

  • Established HeLa cell lines expressing epitope-tagged TRAP/Mediator subunits (MED6, MED7, CDK8).
  • Isolated complexes using affinity and HPLC-gel filtration chromatography.
  • Assessed transcriptional activity in vitro and performed RNA interference knockdown of CDK8.

Main Results:

  • Identified three distinct TRAP/Mediator-like complexes (TMLC1, TMLC2, TMLC3) with varying molecular masses and subunit compositions.
  • TMLC1 and TMLC3 augmented transcription, while TMLC2 repressed it; TMLC1 and TMLC2 phosphorylated RNA polymerase II.
  • Knockdown of CDK8 inhibited transcriptional activation, suggesting a positive role in the process.

Conclusions:

  • Human TRAP/Mediator complexes exhibit structural and functional heterogeneity.
  • CDK8 is implicated in positive regulation of transcriptional activation, potentially through interactions with general transcription factors and RNA polymerase II phosphorylation.

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