title: Ubc9p and the conjugation of SUMO-1 to RanGAP1 and RanBP2.
abstract: 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.
authors.affiliation: Laboratory of Molecular Embryology, NICHD, National Institutes of Health, Building 18, Room 106, Bethesda, Maryland 20892-5431, USA.
authors.forename: H
authors.initials: H
authors.lastname: Saitoh
authors.forename: D B
authors.initials: DB
authors.lastname: Sparrow
authors.forename: T
authors.initials: T
authors.lastname: Shiomi
authors.forename: R T
authors.initials: RT
authors.lastname: Pu
authors.forename: T
authors.initials: T
authors.lastname: Nishimoto
authors.forename: T J
authors.initials: TJ
authors.lastname: Mohun
authors.forename: M
authors.initials: M
authors.lastname: Dasso
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D008025:Ligases / Q000378:metabolism*; D018832:Molecular Chaperones; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D025842:SUMO-1 Protein; D044763:Ubiquitin-Conjugating Enzymes; D014452:Ubiquitins / Q000378:metabolism*; D014981:Xenopus; D029867:Xenopus Proteins; D000098843:Ubiquitin-Conjugating Enzyme UBC9
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D020690:GTPase-Activating Proteins; D018832:Molecular Chaperones; D028861:Nuclear Pore Complex Proteins; D009687:Nuclear Proteins; C513268:RanGAP1 protein, Xenopus; D011993:Recombinant Fusion Proteins; D025842:SUMO-1 Protein; D014452:Ubiquitins; D029867:Xenopus Proteins; C094493:ran-binding protein 2; D044763:Ubiquitin-Conjugating Enzymes; D008025:Ligases; D000098843:Ubiquitin-Conjugating Enzyme UBC9