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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.

http://www.ncbi.nlm.nih.gov/pubmed/9497385

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 RIS Download

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