Nuclear transport of histone 2b in mammalian cells is signal- and energy-dependent and different from the importin alpha/beta-mediated process.
Histone 2b nuclear transport was investigated using the digitonin-permeabilized cell system and the rat liver resealed nuclear envelope system. In permeabilized cells, maximal uptake of histone 2b is dependent on cytosolic components and an appropriate energy source. Addition of the recombinant proteins importin alpha/beta, and Ran, as well as ATP and GTP, to cytosol-depleted permeabilized cells does not enhance the uptake of histone 2b in contrast to that of nucleoplasmin serving as a control. Nuclear import of histone 2b cannot be blocked by addition of an excess of a nuclear localization signal-bearing peptide or nucleoplasmin. Similar results were obtained with resealed nuclear envelopes. As shown previously, resealed vesicles respond to the importin signal for the uptake of nuclear localization signal-bearing proteins which allows investigation of the import mechanism independent of intranuclear binding to chromatin. Uptake of histone 2b therefore seems to be an energy-requiring transport mechanism different from the import of proteins bearing a typical nuclear localization signal.
Institut für Biochemie der Johann Wolfgang Goethe-Universität Frankfurt am Main, Germany. tlanger@stud.uni-frankfurt.de
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D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000818:Animals; D001667:Binding, Competitive / Q000502:physiology; D003600:Cytosol / Q000378:metabolism; D004734:Energy Metabolism / Q000502:physiology*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006367:HeLa Cells; D006657:Histones / Q000378:metabolism*; D006801:Humans; D007457:Iodine Radioisotopes; D028884:Karyopherins; D008099:Liver / Q000166:cytology; D008322:Mammals; D009685:Nuclear Envelope / Q000378:metabolism; D009687:Nuclear Proteins / Q000493:pharmacokinetics*; D009865:Oocytes / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000493:pharmacokinetics; D015398:Signal Transduction / Q000502:physiology*; D014981:Xenopus; D020931:ran GTP-Binding Protein / Q000493:pharmacokinetics
D018840:HSP70 Heat-Shock Proteins; D006657:Histones; D007457:Iodine Radioisotopes; D028884:Karyopherins; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D020931:ran GTP-Binding Protein