title: Combinatorial diversity of fission yeast SCF ubiquitin ligases by homo- and heterooligomeric assemblies of the F-box proteins Pop1p and Pop2p.
abstract: BACKGROUND
  SCF ubiquitin ligases share the core subunits cullin 1, SKP1, and HRT1/RBX1/ROC1, which associate with different F-box proteins. F-box proteins bind substrates following their phosphorylation upon stimulation of various signaling pathways. Ubiquitin-mediated destruction of the fission yeast cyclin-dependent kinase inhibitor Rum1p depends on two heterooligomerizing F-box proteins, Pop1p and Pop2p. Both proteins interact with the cullin Pcu1p when overexpressed, but it is unknown whether this reflects their co-assembly into bona fide SCF complexes.
  
  
  RESULTS
  We have identified Psh1p and Pip1p, the fission yeast homologues of human SKP1 and HRT1/RBX1/ROC1, and show that both associate with Pop1p, Pop2p, and Pcu1p into a ~500 kDa SCFPop1p-Pop2p complex, which supports polyubiquitylation of Rum1p. Only the F-box of Pop1p is required for SCFPop1p-Pop2p function, while Pop2p seems to be attracted into the complex through binding to Pop1p. Since all SCFPop1p-Pop2p subunits, except for Pop1p, which is exclusively nuclear, localize to both the nucleus and the cytoplasm, the F-box of Pop2p may be critical for the assembly of cytoplasmic SCFPop2p complexes. In support of this notion, we demonstrate individual SCFPop1p and SCFPop2p complexes bearing ubiquitin ligase activity.
  
  
  CONCLUSIONS
  Our data suggest that distinct homo- and heterooligomeric assemblies of Pop1p and Pop2p generate combinatorial diversity of SCFPop function in fission yeast. Whereas a heterooligomeric SCFPop1p-Pop2p complex mediates polyubiquitylation of Rum1p, homooligomeric SCFPop1p and SCFPop2p complexes may target unknown nuclear and cytoplasmic substrates.
authors.affiliation: Department of Cancer Cell Biology, Harvard School of Public Health, Boston, MA, USA. vseibert@europroteome.com
authors.forename: Volker
authors.initials: V
authors.lastname: Seibert
authors.forename: Corinna
authors.initials: C
authors.lastname: Prohl
authors.forename: Ida
authors.initials: I
authors.lastname: Schoultz
authors.forename: Edward
authors.initials: E
authors.lastname: Rhee
authors.forename: Rebecca
authors.initials: R
authors.lastname: Lopez
authors.forename: Kareem
authors.initials: K
authors.lastname: Abderazzaq
authors.forename: Chunshui
authors.initials: C
authors.lastname: Zhou
authors.forename: Dieter A
authors.initials: DA
authors.lastname: Wolf
mesh_terms: D001665:Binding Sites; D002451:Cell Compartmentation; D046911:Macromolecular Substances; D009154:Mutation; D010453:Peptide Synthases / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D044843:SKP Cullin F-Box Protein Ligases; D012568:Schizosaccharomyces / Q000201:enzymology* / Q000378:metabolism; D029702:Schizosaccharomyces pombe Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D014452:Ubiquitins / Q000378:metabolism
chemical_list: D046911:Macromolecular Substances; D021122:Protein Subunits; C086077:Rum1 protein, S pombe; D029702:Schizosaccharomyces pombe Proteins; D014452:Ubiquitins; D044843:SKP Cullin F-Box Protein Ligases; D010453:Peptide Synthases