Chromatin-bound NLS proteins recruit membrane vesicles and nucleoporins for nuclear envelope assembly via importin-α/β
Chromatin-bound NLS proteins recruit membrane vesicles and nucleoporins for nuclear envelope assembly via importin-α/β
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DOI：
10.1038/cr.2012.113
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发表时间：
2012-11-01
期刊：
影响因子：
44.1
通讯作者：
Zhang, Chuanmao
中科院分区：
文献类型：
--
作者：
Lu, Quanlong;Lu, Zhigang;Zhang, Chuanmao
核膜（NE）组装的机制尚不完全清楚。 Importin-beta 和小 GTPase Ran 与 NE 组装过程的空间调控有关。在这里，我们报道了在非洲爪蟾卵提取物中 NE 组装过程中，染色质结合的 NLS（核定位序列）蛋白通过 importin-α 和 -β 为 NE 前体膜囊泡和核孔蛋白提供了对接位点。我们发现，随着丰富的 NLS 蛋白（如核蓝蛋白和组蛋白）快速募集到提取物中的脱膜精子染色质，importin-alpha 会快速结合染色质 NLS 蛋白。同时，importin-beta 结合细胞质 NE 前体膜囊泡和核孔蛋白。通过与染色质 NLS 蛋白上的 importin-alpha 相互作用，importin-beta 将膜囊泡和核孔蛋白靶向染色质表面。一旦在 RCC1 生成的染色质上遇到 Ran-GTP，importin-beta 会优先结合 Ran-GTP 并释放膜囊泡和核孔蛋白以进行 NE 组装。通过用过量的可溶性 NLS 蛋白阻断 importin-alpha 和 NLS 蛋白之间的相互作用或通过从提取物中耗尽 importin-beta 来破坏 NE 组装。我们的研究结果揭示了非洲爪蟾卵提取物中 NE 组装的新分子机制。
The mechanism for nuclear envelope (NE) assembly is not fully understood. Importin-beta 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-alpha and -beta 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-alpha binds the chromatin NLS proteins rapidly. Meanwhile, importin-beta binds cytoplasmic NE precursor membrane vesicles and nucleoporins. Through interacting with importin-alpha on the chromatin NLS proteins, importin-beta targets the membrane vesicles and nucleoporins to the chromatin surface. Once encountering Ran-GTP on the chromatin generated by RCC1, importin-beta preferentially binds Ran-GTP and releases the membrane vesicles and nucleoporins for NE assembly. NE assembly is disrupted by blocking the interaction between importin-alpha and NLS proteins with excess soluble NLS proteins or by depletion of importin-beta from the extract. Our findings reveal a novel molecular mechanism for NE assembly in Xenopus egg extracts.