title: Importin 13: a novel mediator of nuclear import and export.
abstract: Importin beta-related receptors mediate translocation through nuclear pore complexes. Co-operation with the RanGTPase system allows them to bind and subsequently release their substrates on opposite sides of the nuclear envelope, which in turn ensures a directed nucleocytoplasmic transport. Here we identify a novel family member from higher eukaryotes that functions primarily, but not exclusively, in import. It accounts for nuclear accumulation of the SUMO-1/sentrin-conjugating enzyme hUBC9 and mediates import of the RBM8 (Y14) protein, and is therefore referred to as importin 13 (Imp13). Unexpectedly, Imp13 also shows export activity towards the translation initiation factor eIF1A and is thus a case where a single importin beta-like receptor transports different substrates in opposite directions. However, Imp13 operates differently from typical exportins in that the binding of eIF1A to Imp13 is only regulated indirectly by RanGTP, and the cytoplasmic release of eIF1A from Imp13 is triggered by the loading of import substrates onto Imp13.
authors.affiliation: ZMBH, INF 282, D-69120 Heidelberg, Germany.
authors.forename: J M
authors.initials: JM
authors.lastname: Mingot
authors.forename: S
authors.initials: S
authors.lastname: Kostka
authors.forename: R
authors.initials: R
authors.lastname: Kraft
authors.forename: E
authors.initials: E
authors.lastname: Hartmann
authors.forename: D
authors.initials: D
authors.lastname: Görlich
mesh_terms: D002467:Cell Nucleus / Q000378:metabolism*; D015977:Eukaryotic Initiation Factor-1; D006367:HeLa Cells; D006801:Humans; D028884:Karyopherins; D008025:Ligases / Q000378:metabolism; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000502:physiology*; D010448:Peptide Initiation Factors / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology*; D016601:RNA-Binding Proteins / Q000378:metabolism; D025842:SUMO-1 Protein; D044763:Ubiquitin-Conjugating Enzymes; D014452:Ubiquitins / Q000378:metabolism; D000098843:Ubiquitin-Conjugating Enzyme UBC9
chemical_list: D015977:Eukaryotic Initiation Factor-1; D028884:Karyopherins; D009687:Nuclear Proteins; D010448:Peptide Initiation Factors; C406243:RBM8A protein, human; D016601:RNA-Binding Proteins; D025842:SUMO-1 Protein; D014452:Ubiquitins; C026022:eukaryotic peptide initiation factor-1A; D044763:Ubiquitin-Conjugating Enzymes; D008025:Ligases; D000098843:Ubiquitin-Conjugating Enzyme UBC9