Siomi M C, Fromont M, Rain J C, Wan L, Wang F, Legrain P, Dreyfuss G
Howard Hughes Medical Institute and Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6148, USA.
Mol Cell Biol. 1998 Jul;18(7):4141-8. doi: 10.1128/MCB.18.7.4141.
Human transportin1 (hTRN1) is the nuclear import receptor for a group of pre-mRNA/mRNA-binding proteins (heterogeneous nuclear ribonucleoproteins [hnRNP]) represented by hnRNP A1, which shuttle continuously between the nucleus and the cytoplasm. hTRN1 interacts with the M9 region of hnRNP A1, a 38-amino-acid domain rich in Gly, Ser, and Asn, and mediates the nuclear import of M9-bearing proteins in vitro. Saccharomyces cerevisiae transportin (yTRN; also known as YBR017c or Kap104p) has been identified and cloned. To understanding the nuclear import mediated by yTRN, we searched with a yeast two-hybrid system for proteins that interact with it. In an exhaustive screen of the S. cerevisiae genome, the most frequently selected open reading frame was the nuclear mRNA-binding protein, Nab2p. We delineated a ca.-50-amino-acid region in Nab2p, termed NAB35, which specifically binds yTRN and is similar to the M9 motif. NAB35 also interacts with hTRN1 and functions as a nuclear localization signal in mammalian cells. Interestingly, yTRN can also mediate the import of NAB35-bearing proteins into mammalian nuclei in vitro. We also report on additional substrates for TRN as well as sequences of Drosophila melanogaster, Xenopus laevis, and Schizosaccharomyces pombe TRNs. Together, these findings demonstrate that both the M9 signal and the nuclear import machinery utilized by the transportin pathway are conserved in evolution.
人类转运蛋白1（hTRN1）是一组以前体mRNA/ mRNA结合蛋白（异质性核糖核蛋白[hnRNP]）为代表的核输入受体，这些蛋白在细胞核和细胞质之间持续穿梭。hTRN1与hnRNP A1的M9区域相互作用，M9区域是一个富含甘氨酸、丝氨酸和天冬酰胺的38个氨基酸的结构域，并在体外介导携带M9的蛋白的核输入。酿酒酵母转运蛋白（yTRN；也称为YBR017c或Kap104p）已被鉴定和克隆。为了了解由yTRN介导的核输入，我们用酵母双杂交系统寻找与之相互作用的蛋白。在对酿酒酵母基因组的详尽筛选中，最常被选中的开放阅读框是核mRNA结合蛋白Nab2p。我们在Nab2p中划定了一个约50个氨基酸的区域，称为NAB35，它特异性结合yTRN，并且与M9基序相似。NAB35也与hTRN1相互作用，并在哺乳动物细胞中作为核定位信号发挥作用。有趣的是，yTRN在体外也能介导携带NAB35的蛋白进入哺乳动物细胞核。我们还报告了TRN的其他底物以及黑腹果蝇、非洲爪蟾和粟酒裂殖酵母TRN的序列。总之，这些发现表明，M9信号和转运蛋白途径所利用的核输入机制在进化中都是保守的。
