Ubc9p and the Conjugation of SUMO-1 to RanGAP1 and RanBP2

Curr Biol. 1998 Jan 15;8(2):121-4. doi: 10.1016/s0960-9822(98)70044-2.


The yeast UBC9 gene encodes a protein with homology to the E2 ubiquitin-conjugating enzymes that mediate the attachment of ubiquitin to substrate proteins [1]. Depletion of Ubc9p arrests cells in G2 or early M phase and stabilizes B-type cyclins [1]. p18(Ubc9), the Xenopus homolog of Ubc9p, associates specifically with p88(RanGAP1) and p340(RanBP2) [2]. Ran-binding protein 2 (p340(RanBP2)) is a nuclear pore protein [3] [4], and p88(RanGAP1) is a modified form of RanGAP1, a GTPase-activating protein for the small GTPase Ran [2]. It has recently been shown that mammalian RanGAP1 can be conjugated with SUMO-1, a small ubiquitin-related modifier [5-7], and that SUMO-1 conjugation promotes RanGAP1's interaction with RanBP2 [2,5,6]. Here we show that p18(Ubc9) acts as an E2-like enzyme for SUMO-1 conjugation, but not for ubiquitin conjugation. This suggests that the SUMO-1 conjugation pathway is biochemically similar to the ubiquitin conjugation pathway but uses a distinct set of enzymes and regulatory mechanisms. We also show that p18(Ubc9) interacts specifically with the internal repeat domain of RanBP2, which is a substrate for SUMO-1 conjugation in Xenopus egg extracts.

MeSH terms

  • Animals
  • Carrier Proteins / metabolism*
  • DNA-Binding Proteins / metabolism*
  • GTPase-Activating Proteins*
  • Ligases / metabolism*
  • Molecular Chaperones
  • Nuclear Pore Complex Proteins*
  • Nuclear Proteins / metabolism*
  • Recombinant Fusion Proteins / metabolism
  • SUMO-1 Protein
  • Ubiquitin-Conjugating Enzymes*
  • Ubiquitins / metabolism*
  • Xenopus
  • Xenopus Proteins


  • Carrier Proteins
  • DNA-Binding Proteins
  • GTPase-Activating Proteins
  • Molecular Chaperones
  • Nuclear Pore Complex Proteins
  • Nuclear Proteins
  • RanGAP1 protein, Xenopus
  • Recombinant Fusion Proteins
  • SUMO-1 Protein
  • Ubiquitins
  • Xenopus Proteins
  • ran-binding protein 2
  • Ubiquitin-Conjugating Enzymes
  • Ligases
  • ubiquitin-conjugating enzyme UBC9

Associated data

  • GENBANK/Z97073