Cyclin C/CDK8 is a novel CTD kinase associated with RNA polymerase II

Oncogene. 1996 Jun 20;12(12):2631-40.


A number of cyclin/kinase complexes have been identified in mammalian cells that are essential for controlled cell proliferation. Cyclin C was isolated by virtue of its ability to rescue the triple CLN mutation in yeast; however, until now its function has remained unclear. Cyclin C associates with a novel cyclin dependent kinase, CDK8, and we demonstrate that this complex is associated with kinase activity towards the carboxy-terminal domain (CTD) of RNA polymerase II. We have identified at least two distinct cyclin C/CDK8 containing complexes within the cell, a larger complex over 500 kD in size, that also contains the largest subunit of RNA polymerase II, and a smaller 170 kD species. Both of these cyclin C complexes retain potent CTD kinase activity. We further demonstrate that the cyclin C/CDK8 complex associates with the large subunit of RNA polymerase II in vivo, implicating a potential role for cyclin C/CDK8 in regulating its activities.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cell Cycle
  • Cells, Cultured
  • Cyclin C
  • Cyclin H
  • Cyclin-Dependent Kinase 8
  • Cyclin-Dependent Kinases*
  • Cyclins / immunology
  • Cyclins / metabolism*
  • Fungal Proteins / metabolism
  • Humans
  • Mice
  • Molecular Sequence Data
  • Protein-Serine-Threonine Kinases / metabolism*
  • RNA Polymerase II / metabolism*
  • Saccharomyces cerevisiae Proteins*
  • Transcription Factors / metabolism


  • CCNC protein, human
  • CCNH protein, human
  • Ccnc protein, mouse
  • Ccnh protein, mouse
  • Cyclin C
  • Cyclin H
  • Cyclins
  • Fungal Proteins
  • Saccharomyces cerevisiae Proteins
  • Transcription Factors
  • SSN8 protein, S cerevisiae
  • Protein-Serine-Threonine Kinases
  • CDK8 protein, human
  • Cyclin-Dependent Kinase 8
  • Cyclin-Dependent Kinases
  • cyclin-dependent kinase-activating kinase
  • SSN3 protein, S cerevisiae
  • RNA Polymerase II