The P446L mutant Drosophila importin-beta (P446L-imp-beta) has been reported to prohibit--in dominant negative fashion--nuclear envelope (NE) assembly. Along elucidating the mode of action of P446L-imp-beta we studied in vitro NE assembly on Sepharose beads. While Drosophila embryo extracts support NE assembly over Sepharose beads coated with Ran, NE assembly does not take place in extracts supplied with exogenous P446L-imp-beta. A NE also forms over importin-beta-coated beads. Surprisingly, when immobilized to Sepharose beads P446L-imp-beta as efficiently recruits NE vesicles as normal importin-beta. The discrepancy in behavior of cytoplasmic and bead-bound P446L-imp-beta appears to be related to icreased--as compared to normal importin-beta--microtubule (MT) binding ability of P446L-imp-beta. While wild-type importin-beta is able to bind MTs and the binding decreases upon RanGTP interaction, P446L-imp-beta cannot be removed from the MTs by RanGTP. P446L-imp-beta, like normal importin-beta, binds some types of the nucleoporins that have been known to be required for NE assembly at the end of mitosis. It appears that the inhibitory effect of P446L-imp-beta on NE assembly is caused by sequestering some of the nucleoporins required for NE assembly to the MTs.

中文翻译：

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P446L-importin-beta通过将核被膜组装因子隔离到微管中来抑制核被膜组装。

据报道，P446L突变果蝇importin-beta（P446L-imp-beta）禁止（以显性负向方式）组装核包膜（NE）。通过阐明P446L-imp-beta的作用方式，我们研究了琼脂糖珠上的体外NE组装。果蝇胚胎提取物在涂有Ran的Sepharose珠上支持NE组装，但在外源P446L-imp-beta提供的提取物中不会发生NE组装。NE也形成在importin-beta包被的珠上。出人意料的是，当固定在琼脂糖凝胶珠上时，P446L-imp-beta可以有效地募集NE囊泡作为正常的importin-beta。与正常的importin-beta-P446L-imp-beta的微管（MT）结合能力相比，胞质和与珠子结合的P446L-imp-beta的行为差异似乎与增加有关。尽管野生型importin-beta能够结合MT，并且在RanGTP相互作用后结合力降低，但RanGTP无法从MT移除P446L-imp-beta。与正常的importin-beta一样，P446L-imp-beta结合某些类型的核孔蛋白，这些核孔蛋白已知是有丝分裂结束时NE组装所必需的。看来，P446L-imp-beta对NE组装的抑制作用是由于将NE组装所需的一些核孔蛋白螯合到MT上引起的。