Schröder H C, Facy P, Monsigny M, Pfeifer K, Bek A, Müller W E
Institut für Physiologische Chemie, Universität Mainz, Federal Republic of Germany.
Eur J Biochem. 1992 May 1;205(3):1017-25. doi: 10.1111/j.1432-1033.1992.tb16869.x.
A nuclear carbohydrate-binding protein with a molecular mass of 67 kDa (CBP67), which is specific for glucose residues, was purified to essential homogeneity from rat liver nuclear extracts. This protein could also be isolated from nuclear ribonucleoprotein (RNP) complexes by extraction in the presence of 0.6 M or 2 M NaCl, but it was absent in polysomal RNP complex. The binding of the purified protein, which has an isoelectric point of 7.3, to glucose-containing glycoconjugates depends on the presence of Ca2+ and Mg2+. Using closed nuclear envelope vesicles as a system to study nuclear transport of RNA, it was shown that both entrapped polysomal mRNA and nuclear RNA precursors are readily exported from the vesicles in an ATP-dependent manner. The transport was unidirectional and strongly promoted by the poly(A) segment attached to these RNAs. In contrast, nuclear RNP complexes entrapped into the vesicles together with glucose-conjugated bovine serum albumin or nucleoplasmin, or bird nest glycoprotein, were not exported into the extravesicular space. However, transport of nuclear RNP complexes could be achieved in the presence of glucose or after co-addition of a glucose-recognizing lectin from Pellina semitubulosa. In Western blots, radioiodinated CBP67 binds to an 80-kDa polypeptide both in isolated rat liver nuclear envelopes and pore-complex laminae. From these results we postulate that CBP67 may direct nuclear RNP complexes to the nuclear pore.
一种分子量为67 kDa的核碳水化合物结合蛋白（CBP67），它对葡萄糖残基具有特异性，已从大鼠肝脏核提取物中纯化至基本同质。该蛋白也可在0.6 M或2 M NaCl存在下通过提取从核糖核蛋白（RNP）复合物中分离出来，但在多聚核糖体RNP复合物中不存在。纯化后的蛋白等电点为7.3，它与含葡萄糖的糖缀合物的结合依赖于Ca2+和Mg2+的存在。利用封闭的核被膜囊泡作为研究RNA核运输的系统，结果表明，被困在囊泡中的多聚核糖体mRNA和核RNA前体都能以ATP依赖的方式从囊泡中顺利输出。这种运输是单向的，并且这些RNA上附着的聚（A）片段能强烈促进运输。相比之下，与葡萄糖缀合的牛血清白蛋白或核纤层蛋白或燕窝糖蛋白一起被困在囊泡中的核RNP复合物不会输出到囊泡外空间。然而，在有葡萄糖存在的情况下或在共同添加来自半管佩利纳的葡萄糖识别凝集素后，核RNP复合物的运输可以实现。在蛋白质免疫印迹中，放射性碘化的CBP67在分离的大鼠肝脏核被膜和孔复合物薄片中均与一种80 kDa的多肽结合。根据这些结果，我们推测CBP67可能将核RNP复合物导向核孔。
