Importin β Negatively Regulates Nuclear Membrane Fusion and Nuclear Pore Complex Assembly

• DOI: 10.1091/mbc.e03-05-0275
• Publication Date: 2003-08-12T02:37:42Z
• Authors: Amnon Harel; Rene C. Chan; Aurelie Lachish-Z...; Ella Zimmerman; Michael Elbaum; Douglass J. Forbes
• Keywords: Importin; Ran; Nuclear pore; Inner membrane; Nuclear membrane

Assembly of a eukaryotic nucleus involves three distinct events: membrane recruitment, fusion to form double nuclear membrane, and pore complex (NPC) assembly. We report that importin beta negatively regulates two these events, NPC When excess is added full Xenopus reconstitution reaction, vesicles are recruited chromatin but their blocked. The down-regulation Ran-GTP reversible. Indeed, RanGTP (RanQ69L) alone stimulates excessive fusion, leading intranuclear tubules cytoplasmic annulate lamellae-like structures. propose precise balance Ran required create correct simultaneously repress undesirable events. Interestingly, truncated 45-462 allows produces nuclei lacking any NPCs. This reveals beta-regulation Excess full-length act similarly when prefused intermediates, i.e., both block block, which maps downstream GTPgammaS BAPTA-sensitive steps in assembly, reversible by cytosol. Remarkably, it not 25 microM RanGTP, concentration easily reverses inhibition. report, using system natural substrates, significantly expands the repertoire beta. Its roles now encompass negative regulation major events assembly: