Richards S A, Lounsbury K M, Carey K L, Macara I G
Department of Pathology, University of Vermont, Burlington 05405-0068, USA.
J Cell Biol. 1996 Sep;134(5):1157-68. doi: 10.1083/jcb.134.5.1157.
RanBP1 is a Ran/TC4 binding protein that can promote the interaction between Ran and beta-importin /beta-karyopherin, a component of the docking complex for nuclear protein cargo. This interaction occurs through a Ran binding domain (RBD). Here we show that RanBP1 is primarily cytoplasmic, but the isolated RBD accumulates in the nucleus. A region COOH-terminal to the RBD is responsible for this cytoplasmic localization. This domain acts heterologously, localizing a nuclear cyclin B1 mutant to the cytoplasm. The domain contains a nuclear export signal that is necessary but not sufficient for the nuclear export of a functional RBD In transiently transfected cells, epitope-tagged RanBP1 promotes dexamethasone-dependent nuclear accumulation of a glucocorticoid receptor-green fluorescent protein fusion, but the isolated RBD potently inhibits this accumulation. The cytosolic location of RanBP1 may therefore be important for nuclear protein import. RanBP1 may provide a key link between the nuclear import and export pathways.
RanBP1是一种Ran/TC4结合蛋白，它能够促进Ran与β-输入蛋白/β-核转运蛋白之间的相互作用，β-输入蛋白/β-核转运蛋白是核蛋白货物对接复合体的一个组成部分。这种相互作用通过一个Ran结合结构域（RBD）发生。在此我们表明，RanBP1主要位于细胞质中，但分离出的RBD在细胞核中积累。RBD羧基末端的一个区域负责这种细胞质定位。该结构域具有异源作用，可将核周期蛋白B1突变体定位到细胞质中。该结构域包含一个核输出信号，这对于功能性RBD的核输出是必要的，但并不充分。在瞬时转染的细胞中，表位标记的RanBP1促进糖皮质激素受体-绿色荧光蛋白融合体的地塞米松依赖性核积累，但分离出的RBD强烈抑制这种积累。因此，RanBP1的胞质定位可能对核蛋白输入很重要。RanBP1可能在核输入和输出途径之间提供关键联系。
