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Identification of human cyclin-dependent kinase 8, a putative protein kinase partner for cyclin C

J P Tassan1, M Jaquenoud, P Léopold

  • 1Swiss Institute for Experimental Cancer Research (ISREC), Epalinges.

Proceedings of the National Academy of Sciences of the United States of America
|September 12, 1995
PubMed

Insights

Researchers identified a human protein kinase, K35 (cyclin-dependent kinase 8 or CDK8), as a likely partner for cyclin C. This cyclin C-CDK8 complex may associate with the mammalian transcription apparatus, potentially relaying growth signals.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Biochemistry

Background:

  • Metazoan cyclin C was initially identified for its role in rescuing yeast cell cycle deficiencies.
  • Understanding cyclin C's function was limited by the absence of its kinase partner.
  • Previous research suggested a potential role for cyclin C in cell cycle control.

Purpose of the Study:

  • To identify the physiological kinase partner of human cyclin C.
  • To investigate the interaction between cyclin C and its potential kinase partner.
  • To explore the functional association of the cyclin C-kinase complex in mammalian cells.

Main Methods:

  • In vitro translation of cyclin-dependent kinases (CDKs) and cyclins to demonstrate specific interactions.
  • Immunoprecipitation of K35 (CDK8) from HeLa cell extracts to detect associated cyclin C.
  • Structural and functional comparisons with the yeast SRB10-SRB11 CDK-cyclin pair.

Main Results:

  • A human protein kinase, K35 (CDK8), was identified as a likely physiological partner of cyclin C.
  • Specific in vitro interactions between K35 and cyclin C were demonstrated.
  • Cyclin C was detected in K35 immunoprecipitates from HeLa cells, confirming in vivo complex formation.
  • The K35-cyclin C complex shows structural similarity to the yeast SRB10-SRB11 complex.

Conclusions:

  • Human K35 (CDK8) and cyclin C form a complex in vivo.
  • This complex is structurally related to a component of the yeast RNA polymerase II holoenzyme.
  • The K35-cyclin C complex is proposed to be functionally associated with the mammalian transcription apparatus.
  • This association may play a role in relaying growth-regulatory signals.

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