NapA and NapB are the Aspergillus nidulans Nap/SET family members and NapB is a nuclear protein specifically interacting with importin alpha.
In eukaryotic cells, importin alpha is the major carrier for transport protein cargoes into the nucleus. We characterize here kapA, the single Aspergillus nidulans gene encoding an importin alpha. Using an affinity approach, we identify six potential interactors of KapA(50), a deleted version of KapA lacking the autoinhibitory importin-beta-binding domain. One such interactor is NapB, the A. nidulans orthologue of Saccharomyces cerevisiae Vps75p, a histone chaperone member of the Nap/SET family of proteins that additionally plays a cytosolic role in vacuolar protein sorting. NapB, but not its close relative NapA (the A. nidulans orthologue of yeast Nap1p) interacts directly with KapA(50) in pull down assays, despite the fact that NapB does not contain a classical nuclear localization sequence. NapB is a nuclear protein which exits nuclei at the onset of mitosis when two simultaneous mechanisms might be acting, the partial disassembly of the nuclear pore complexes and as yet unidentified posttranslational modification of NapB. The mitotic cytosolic localization of NapB might facilitate its putative role in the sorting of protein cargoes to the vacuole. In addition, we show that NapB and the mitotic B-type cyclin NimE compete for in vitro binding to KapA.
Araújo-Bazán
Lidia
L
Departamento de Microbiología Molecular, Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu, 9, Madrid 28040, Spain.
Fernández-Martínez
Javier
J
Ríos
Vivian Maythe de Los
VM
Etxebeste
Oier
O
Albar
Juan Pablo
JP
Peñalva
Miguel Angel
MA
Espeso
Eduardo Antonio
EA
D021581:Active Transport, Cell Nucleus; D001233:Aspergillus nidulans / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D002846:Chromatography, Affinity; D003593:Cytoplasm / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D008938:Mitosis / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D028901:alpha Karyopherins / Q000235:genetics / Q000378:metabolism*
D005656:Fungal Proteins; D009687:Nuclear Proteins; D028901:alpha Karyopherins