Mammalian mediator subunit mMED8 is an Elongin BC-interacting protein that can assemble with Cul2 and Rbx1 to reconstitute a ubiquitin ligase

Proc Natl Acad Sci U S A. 2002 Aug 6;99(16):10353-8. doi: 10.1073/pnas.162424199. Epub 2002 Jul 29.

Abstract

The heterodimeric Elongin BC complex has been shown to interact in vitro and in cells with a conserved BC-box motif found in an increasing number of proteins including RNA polymerase II elongation factor Elongin A, suppressor of cytokine signaling (SOCS)-box proteins, and the von Hippel-Lindau tumor suppressor protein. Recently, the Elongin BC complex was found to function as an adaptor that links these BC-box proteins to a module composed of Cullin family members Cul2 or Cul5 and RING-H2 finger protein Rbx1 to reconstitute a family of E3 ubiquitin ligases that activate ubiquitylation by the E2 ubiquitin-conjugating enzyme Ubc5. As part of our effort to understand the functions of Elongin BC-based ubiquitin ligases, we exploited a modified yeast two-hybrid screen to identify a mammalian BC-box protein similar in sequence to Saccharomyces cerevisiae Mediator subunit Med8p. In this report we demonstrate (i) that mammalian MED8 is a subunit of the mammalian Mediator complex and (ii) that MED8 can assemble with Elongins B and C, Cul2, and Rbx1 to reconstitute a ubiquitin ligase. Taken together, our findings are consistent with the model that MED8 could function to recruit ubiquitin ligase activity directly to the RNA polymerase II transcriptional machinery.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Binding Sites
  • Cell Cycle Proteins / metabolism*
  • Cell Line
  • Cell Line, Transformed
  • Cullin Proteins*
  • DNA, Complementary
  • Dimerization
  • Elongin
  • Fungal Proteins / metabolism
  • Humans
  • Ligases / genetics
  • Ligases / metabolism*
  • Liver / metabolism
  • Mammals
  • Mediator Complex
  • Mice
  • Molecular Sequence Data
  • Nuclear Proteins / metabolism
  • Rats
  • Saccharomyces cerevisiae Proteins*
  • Spodoptera
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Tumor Suppressor Proteins / metabolism
  • Ubiquitin-Conjugating Enzymes*
  • Ubiquitin-Protein Ligases*
  • Von Hippel-Lindau Tumor Suppressor Protein

Substances

  • CUL2 protein, human
  • Cell Cycle Proteins
  • Cullin Proteins
  • DNA, Complementary
  • ELOA protein, human
  • Eloa protein, mouse
  • Eloa protein, rat
  • Elongin
  • Fungal Proteins
  • MED8 protein, rat
  • Mediator Complex
  • NUT2 protein, S cerevisiae
  • Nuclear Proteins
  • Saccharomyces cerevisiae Proteins
  • Transcription Factors
  • Tumor Suppressor Proteins
  • UBC5 protein, S cerevisiae
  • Ubiquitin-Conjugating Enzymes
  • Ubiquitin-Protein Ligases
  • Von Hippel-Lindau Tumor Suppressor Protein
  • Ligases
  • VHL protein, human

Associated data

  • GENBANK/AF521562