title: Nuclear import of histone H2A and H2B is mediated by a network of karyopherins.
abstract: The first step in the assembly of new chromatin is the cell cycle-regulated synthesis and nuclear import of core histones. The core histones include H2A and H2B, which are assembled into nucleosomes as heterodimers. We show here that the import of histone H2A and H2B is mediated by several members of the karyopherin (Kap; importin) family. An abundant complex of H2A, H2B, and Kap114p was detected in cytosol. In addition, two other Kaps, Kap121p and Kap123p, and the histone chaperone Nap1p were isolated with H2A and H2B. Nap1p is not necessary for the formation of the Kap114p-H2A/H2B complex or for import of H2A and H2B. We demonstrate that both histones contain a nuclear localization sequence (NLS) in the amino-terminal tail. Fusions of the NLSs to green fluorescent protein were specifically mislocalized to the cytoplasm in kap mutant strains. In addition, we detected a specific mislocalization in a kap95 temperature-sensitive strain, suggesting that this Kap is also involved in the import of H2A and H2B in vivo. Importantly, we show that Kap114p, Kap121p, and Kap95 interact directly with both histone NLSs and that RanGTP inhibits this association. These data suggest that the import of H2A and H2B is mediated by a network of Kaps, in which Kap114p may play the major role.
authors: Center for Cell Signaling, Department of Microbiology, Health Sciences Center, University of Virginia, 22908, USA.
authors: N
authors: N
authors: Mosammaparast
authors: K R
authors: KR
authors: Jackson
authors: Y
authors: Y
authors: Guo
authors: C J
authors: CJ
authors: Brame
authors: J
authors: J
authors: Shabanowitz
authors: D F
authors: DF
authors: Hunt
authors: L F
authors: LF
authors: Pemberton
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D018797:Cell Cycle Proteins; D002467:Cell Nucleus / Q000378:metabolism*; D017930:Genes, Reporter; D006657:Histones / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D046911:Macromolecular Substances; D008856:Microscopy, Fluorescence; D018832:Molecular Chaperones / Q000378:metabolism*; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D056490:Nucleosome Assembly Protein 1; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D015003:Yeasts / Q000235:genetics / Q000378:metabolism; D028961:beta Karyopherins
chemical_list: D018797:Cell Cycle Proteins; D006657:Histones; C400425:KAP114 protein, S cerevisiae; D046911:Macromolecular Substances; D018832:Molecular Chaperones; C533556:NAP1 protein, S cerevisiae; C533557:NAP1L1 protein, human; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D056490:Nucleosome Assembly Protein 1; D011506:Proteins; D011993:Recombinant Fusion Proteins; D029701:Saccharomyces cerevisiae Proteins; D028961:beta Karyopherins