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キーワード:
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要旨:
Nuclear pore complexes (NPCs) are large protein assemblies located within the nuclear envelope. They function as barriers and regulators of molecule transit between the cytoplasm and the nucleoplasm. NPCs assemble in two distinct stages of the cell cycle: after mitosis and throughout the whole of interphase. The nucleoporin Nup50 is localized on the nucleoplasmic side of the pore during interphase and is well known as an auxiliary factor in nuclear transport: in fact, it binds transport receptors as well as the small GTPase Ran, key components of the NLS-containing cargo import machinery. In addition to this well-studied function, we have determined that successful assembly of NPCs at the end of mitosis requires Nup50: depletion of the protein in Xenopus egg extract blocks NPC assembly in vitro, whereas formation of nuclear envelope is unaffected. A similar phenotype has previously been described for Mel28/ELYS depletion, which is required for the same process and which tethers components of the core NPC onto the decondensing chromatin in the early stages of the nuclear assembly. However, our experiments show that Nup50 and Mel28 function independently in NPC assembly. Thus, this work establishes that Nup50 is critically involved in NPC assembly at the end of mitosis in a separate event that occurs in parallel and probably simultaneously to Mel28/ELYS mediated chromatin seeding of NPC core components.
