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Transportin Regulates Major Mitotic Assembly Events: From Spindle to Nuclear Pore Assembly

机译:运输蛋白调节有丝分裂大会的重大事件:从纺锤到核孔装配。

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摘要

Mitosis in higher eukaryotes is marked by the sequential assembly of two massive structures: the mitotic spindle and the nucleus. Nuclear assembly itself requires the precise formation of both nuclear membranes and nuclear pore complexes. Previously, importin alpha/beta and RanGTP were shown to act as dueling regulators to ensure that these assembly processes occur only in the vicinity of the mitotic chromosomes. We now find that the distantly related karyopherin, transportin, negatively regulates nuclear envelope fusion and nuclear pore assembly in Xenopus egg extracts. We show that transportin—and importin beta—initiate their regulation as early as the first known step of nuclear pore assembly: recruitment of the critical pore-targeting nucleoporin ELYS/MEL-28 to chromatin. Indeed, each karyopherin can interact directly with ELYS. We further define the nucleoporin subunit targets for transportin and importin beta and find them to be largely the same: ELYS, the Nup107/160 complex, Nup53, and the FG nucleoporins. Equally importantly, we find that transportin negatively regulates mitotic spindle assembly. These negative regulatory events are counteracted by RanGTP. We conclude that the interplay of the two negative regulators, transportin and importin beta, along with the positive regulator RanGTP, allows precise choreography of multiple cell cycle assembly events.
机译:高等真核生物中的有丝分裂以两个块状结构的顺序组装为特征:有丝分裂纺锤体和核。核组装本身需要精确形成核膜和核孔复合体。以前,importin alpha / beta和RanGTP被显示为对决调节子,以确保这些组装过程仅在有丝分裂染色体附近发生。现在我们发现,与之密切相关的核转运蛋白运输蛋白对非洲爪蟾卵提取物中的核包膜融合和核孔组装具有负调节作用。我们显示,transportin和importin beta最早在核孔装配的第一个已知步骤中就开始了对它们的调节:将关键的靶向孔的核孔蛋白ELYS / MEL-28募集到染色质中。实际上,每个核蛋白都可以与ELYS直接相互作用。我们进一步定义了transportin和importin beta的核孔蛋白亚基靶标,发现它们基本相同:ELYS,Nup107 / 160复合物,Nup53和FG核孔蛋白。同样重要的是,我们发现transportin负调节有丝分裂纺锤体组装。这些负面的监管事件被RanGTP抵消了。我们得出结论,两个负调节剂,transportin和importin beta的相互作用,以及正调节剂RanGTP,可以对多个细胞周期装配事件进行精确的编排。

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