title: A role for nucleosome assembly protein 1 in the nuclear transport of histones H2A and H2B.
abstract: Import of core histones into the nucleus is a prerequisite for their deposition onto DNA and the assembly of chromatin. Here we demonstrate that nucleosome assembly protein 1 (Nap1p), a protein previously implicated in the deposition of histones H2A and H2B, is also involved in the transport of these two histones. We demonstrate that Nap1p can bind directly to Kap114p, the primary karyopherin/importin responsible for the nuclear import of H2A and H2B. Nap1p also serves as a bridge between Kap114p and the histone nuclear localization sequence (NLS). Nap1p acts cooperatively to increase the affinity of Kap114p for these NLSs. Nuclear accumulation of histone NLS-green fluorescent protein (GFP) reporters was decreased in deltanap1 cells. Furthermore, we demonstrate that Nap1p promotes the association of the H2A and H2B NLSs specifically with the karyopherin Kap114p. Localization studies demonstrate that Nap1p is a nucleocytoplasmic shuttling protein, and genetic experiments suggest that its shuttling is important for maintaining chromatin structure in vivo. We propose a model in which Nap1p links the nuclear transport of H2A and H2B to chromatin assembly.
authors.affiliation: Center for Cell Signaling, University of Virginia, Charlottesville, VA 22908, USA.
authors.forename: Nima
authors.initials: N
authors.lastname: Mosammaparast
authors.forename: Courtney S
authors.initials: CS
authors.lastname: Ewart
authors.forename: Lucy F
authors.initials: LF
authors.lastname: Pemberton
mesh_terms: D021581:Active Transport, Cell Nucleus; D018797:Cell Cycle Proteins; D002467:Cell Nucleus / Q000378:metabolism*; D006657:Histones / Q000378:metabolism*; D066298:In Vitro Techniques; D028884:Karyopherins / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D056490:Nucleosome Assembly Protein 1; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism*; D018626:Retroelements / Q000235:genetics; 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; D028884:Karyopherins; C533556:NAP1 protein, S cerevisiae; D009687:Nuclear Proteins; D056490:Nucleosome Assembly Protein 1; D011506:Proteins; D018626:Retroelements; D029701:Saccharomyces cerevisiae Proteins; D028961:beta Karyopherins