Romac J M, Graff D H, Keene J D
Department of Microbiology, Duke University Medical Center, Durham, North Carolina 27710.
Mol Cell Biol. 1994 Jul;14(7):4662-70. doi: 10.1128/mcb.14.7.4662-4670.1994.
Expression of the recombinant human U1-70K protein in COS cells resulted in its rapid transport to the nucleus, even when binding to U1 RNA was debilitated. Deletion analysis of the U1-70K protein revealed the existence of two segments of the protein which were independently capable of nuclear localization. One nuclear localization signal (NLS) was mapped within the U1 RNA-binding domain and consists of two typically separated but interdependent elements. The major element of this NLS resides in structural loop 5 between the beta 4 strand and the alpha 2 helix of the folded RNA recognition motif. The C-terminal half of the U1-70K protein which was capable of nuclear entry contains two arginine-rich regions, which suggests the existence of a second NLS. Site-directed mutagenesis of the RNA recognition motif NLS demonstrated that the U1-70K protein can be transported independently of U1 RNA and that its association with the U1 small nuclear ribonucleoprotein particle can occur in the nucleus.
重组人U1 - 70K蛋白在COS细胞中的表达导致其迅速转运至细胞核，即便其与U1 RNA的结合能力减弱时亦是如此。对U1 - 70K蛋白的缺失分析揭示该蛋白存在两个能够独立进行核定位的区段。一个核定位信号（NLS）定位于U1 RNA结合结构域内，由两个通常分离但相互依存的元件组成。此NLS的主要元件位于折叠的RNA识别基序的β4链与α2螺旋之间的结构环5中。能够进入细胞核的U1 - 70K蛋白的C末端一半包含两个富含精氨酸的区域，这表明存在第二个NLS。对RNA识别基序NLS进行定点诱变表明，U1 - 70K蛋白能够独立于U1 RNA进行转运，并且其与U1小核核糖核蛋白颗粒的缔合能够在细胞核中发生。
