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The RING finger protein Siah-1 regulates the level of the transcriptional coactivator OBF-1.

The transcriptional coactivator OBF-1, which interacts with Oct-1 and Oct-2 and the octamer site DNA, has been shown to be critical for development of a normal immune response and the formation of germinal centers in secondary lymphoid organs. Here we have identified the RING finger protein Siah-1 as a protein interacting specifically with OBF-1. This interaction is mediated by the C-terminal part of Siah-1 and by residues in the N-terminus of OBF-1, partly distinct from the residues required for formation of a complex with the Oct POU domains and the DNA. Interaction between Siah-1 and OBF-1 leads to downregulation of OBF-1 protein level but not mRNA, and to a corresponding reduction in octamer site-dependent transcription activation. Inhibition of the ubiquitin-proteasome pathway in B cells leads to elevated levels of OBF-1 protein. Furthermore, in immunized mice, OBF-1 protein amounts are dramatically increased in primary activated B cells, without concomitant increase in OBF-1 mRNA. These data suggest that Siah-1 is part of a novel regulatory loop controlling the level of OBF-1 protein in B cells.

Pubmed ID: 11483517


  • Tiedt R
  • Bartholdy BA
  • Matthias G
  • Newell JW
  • Matthias P


The EMBO journal

Publication Data

August 1, 2001

Associated Grants


Mesh Terms

  • Amino Acid Sequence
  • Animals
  • B-Lymphocytes
  • Binding Sites
  • Boronic Acids
  • Cell Line
  • Cell Line, Transformed
  • Cysteine Endopeptidases
  • Cysteine Proteinase Inhibitors
  • Down-Regulation
  • Humans
  • Mice
  • Molecular Sequence Data
  • Multienzyme Complexes
  • Nuclear Proteins
  • Proteasome Endopeptidase Complex
  • RNA Processing, Post-Transcriptional
  • Trans-Activators
  • Transcriptional Activation
  • Ubiquitin-Protein Ligases
  • Ubiquitins
  • Up-Regulation
  • Zinc Fingers