Chromatin-bound NLS proteins recruit membrane vesicles and nucleoporins for nuclear envelope assembly via importin-α/β

Cell Res. 2012 Nov;22(11):1562-75. doi: 10.1038/cr.2012.113. Epub 2012 Jul 31.


The mechanism for nuclear envelope (NE) assembly is not fully understood. Importin-β and the small GTPase Ran have been implicated in the spatial regulation of NE assembly process. Here we report that chromatin-bound NLS (nuclear localization sequence) proteins provide docking sites for the NE precursor membrane vesicles and nucleoporins via importin-α and -β during NE assembly in Xenopus egg extracts. We show that along with the fast recruitment of the abundant NLS proteins such as nucleoplasmin and histones to the demembranated sperm chromatin in the extracts, importin-α binds the chromatin NLS proteins rapidly. Meanwhile, importin-β binds cytoplasmic NE precursor membrane vesicles and nucleoporins. Through interacting with importin-α on the chromatin NLS proteins, importin-β targets the membrane vesicles and nucleoporins to the chromatin surface. Once encountering Ran-GTP on the chromatin generated by RCC1, importin-β preferentially binds Ran-GTP and releases the membrane vesicles and nucleoporins for NE assembly. NE assembly is disrupted by blocking the interaction between importin-α and NLS proteins with excess soluble NLS proteins or by depletion of importin-β from the extract. Our findings reveal a novel molecular mechanism for NE assembly in Xenopus egg extracts.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Cycle Proteins / metabolism
  • Chromatin / metabolism*
  • Guanine Nucleotide Exchange Factors / metabolism
  • HeLa Cells
  • Humans
  • Nuclear Envelope / metabolism*
  • Nuclear Localization Signals / metabolism*
  • Nuclear Pore Complex Proteins / metabolism*
  • Nuclear Proteins / genetics
  • Nuclear Proteins / metabolism
  • Xenopus / genetics
  • Xenopus / metabolism
  • Xenopus Proteins / metabolism
  • alpha Karyopherins / metabolism*
  • beta Karyopherins / metabolism*
  • ran GTP-Binding Protein / metabolism


  • Cell Cycle Proteins
  • Chromatin
  • Guanine Nucleotide Exchange Factors
  • Nuclear Localization Signals
  • Nuclear Pore Complex Proteins
  • Nuclear Proteins
  • RCC1 protein, Xenopus
  • Xenopus Proteins
  • alpha Karyopherins
  • beta Karyopherins
  • ran GTP-Binding Protein