title: The DNA topoisomerase I binding protein topors as a novel cellular target for SUMO-1 modification: characterization of domains necessary for subcellular localization and sumolation.
abstract: Over the past years, modification by covalent attachment of SUMO (small ubiquitin-like modifier) has been demonstrated for of a number of cellular and viral proteins. While increasing evidence suggests a role for SUMO modification in the regulation of protein-protein interactions and/or subcellular localization, most SUMO targets are still at large. In this report we show that Topors, a Topoisomerase I and p53 interacting protein of hitherto unknown function, presents a novel cellular target for SUMO-1 modification. In a yeast two-hybrid system, Topors interacted with both SUMO-1 and the SUMO-1 conjugating enzyme UBC9. Multiple SUMO-1 modified forms of Topors could be detected after cotransfection of exogenous SUMO-1 and Topors induced the colocalization of a YFP tagged SUMO-1 protein in a speckled pattern in the nucleus. A subset of these Topors' nuclear speckles were closely associated with the PML nuclear bodies (POD, ND10). A central domain comprising Topors residues 437 to 574 was sufficient for both sumolation and localization to nuclear speckles. One SUMO-1 acceptor site at lysine residue 560 could be identified within this region. However, sumolation-deficient Topors mutants showed that sumolation obviously is not required for localization to nuclear speckles.
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D001426:Bacterial Proteins; D001665:Binding Sites / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002451:Cell Compartmentation / Q000502:physiology*; D002467:Cell Nucleus / Q000201:enzymology* / Q000648:ultrastructure; D022003:Cell Nucleus Structures / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005057:Eukaryotic Cells / Q000201:enzymology* / Q000648:ultrastructure; D006367:HeLa Cells; D006801:Humans; D008025:Ligases / Q000378:metabolism; D008164:Luminescent Proteins; D009154:Mutation / Q000235:genetics; D009363:Neoplasm Proteins; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary / Q000502:physiology; D025842:SUMO-1 Protein / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases; D000098843:Ubiquitin-Conjugating Enzyme UBC9
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D008164:Luminescent Proteins; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D025842:SUMO-1 Protein; D014157:Transcription Factors; C054562:yellow fluorescent protein, Bacteria; D044763:Ubiquitin-Conjugating Enzymes; C120157:TOPORS protein, human; D044767:Ubiquitin-Protein Ligases; D008025:Ligases; D000098843:Ubiquitin-Conjugating Enzyme UBC9