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Modification of Ran GTPase-activating protein by the small ubiquitin-related modifier SUMO-1 requires Ubc9, an E2-type ubiquitin-conjugating enzyme homologue.

Covalent modification of the Ran GTPase-activating protein RanGAP1 with the ubiquitin-related protein SUMO-1 promotes its association with Nup358, a component of the cytoplasmic fibrils emanating from the nuclear pore complex (1,2). In Xenopus egg extracts, Nup358 can be found in a complex with Ubc9 (3), a structural homologue of the E2-type ubiquitin-conjugating enzymes (UBCs). Here we show that a subset of the human homologue of Ubc9 (HsUbc9) colocalizes with RanGAP1 at the nuclear envelope. HsUbc9 forms thiolester conjugates with recombinant SUMO-1, but not with recombinant ubiquitin, indicating that it is functionally distinct from E2-type UBCs. Finally, HsUbc9 is required for the modification of RanGAP1 by SUMO-1. These results suggest that HsUbc9 is a component of a novel enzymatic cascade that modifies RanGAP1, and possibly other substrates, with SUMO-1.

Pubmed ID: 9497385


  • Lee GW
  • Melchior F
  • Matunis MJ
  • Mahajan R
  • Tian Q
  • Anderson P


The Journal of biological chemistry

Publication Data

March 13, 1998

Associated Grants


Mesh Terms

  • Adenosine Triphosphate
  • Animals
  • Binding Sites
  • Carrier Proteins
  • GTPase-Activating Proteins
  • Humans
  • Ligases
  • Mutation
  • Nuclear Envelope
  • Precipitin Tests
  • Protein Binding
  • Rats
  • SUMO-1 Protein
  • Substrate Specificity
  • Sulfhydryl Compounds
  • Ubiquitin-Conjugating Enzymes
  • Ubiquitins
  • Xenopus Proteins