Mammalian mediator subunit mMED8 is an Elongin BC-interacting protein that can assemble with Cul2 and Rbx1 to reconstitute a ubiquitin ligase.
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.
Mesh Terms:
Amino Acid Sequence, Animals, Base Sequence, Binding Sites, Cell Cycle Proteins, Cell Line, Cell Line, Transformed, Cullin Proteins, DNA, Complementary, Dimerization, Fungal Proteins, Humans, Ligases, Liver, Mammals, Mediator Complex, Mice, Molecular Sequence Data, Nuclear Proteins, Rats, Saccharomyces cerevisiae Proteins, Spodoptera, Transcription Factors, Tumor Suppressor Proteins, Ubiquitin-Conjugating Enzymes, Ubiquitin-Protein Ligases, Von Hippel-Lindau Tumor Suppressor Protein
Amino Acid Sequence, Animals, Base Sequence, Binding Sites, Cell Cycle Proteins, Cell Line, Cell Line, Transformed, Cullin Proteins, DNA, Complementary, Dimerization, Fungal Proteins, Humans, Ligases, Liver, Mammals, Mediator Complex, Mice, Molecular Sequence Data, Nuclear Proteins, Rats, Saccharomyces cerevisiae Proteins, Spodoptera, Transcription Factors, Tumor Suppressor Proteins, Ubiquitin-Conjugating Enzymes, Ubiquitin-Protein Ligases, Von Hippel-Lindau Tumor Suppressor Protein
Proc. Natl. Acad. Sci. U.S.A.
Date: Aug. 06, 2002
PubMed ID: 12149480
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