He X P, Bataillé N, Fried H M
Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill 27599.
J Cell Sci. 1994 Apr;107 ( Pt 4):903-12. doi: 10.1242/jcs.107.4.903.
The signal recognition particle is a cytoplasmic RNA-protein complex that mediates translocation of secretory polypeptides into the endoplasmic reticulum. We have used a Xenopus oocyte microinjection assay to determine how signal recognition particle (SRP) RNA is exported from the nucleus. Following nuclear injection, SRP RNA accumulated in the cytoplasm while cytoplasmically injected SRP RNA did not enter the nucleus. Cytoplasmic accumulation of SRP RNA was an apparently facilitated process dependent on limiting trans-acting factors, since nuclear export exhibited saturation kinetics and was completely blocked either at low temperature or by wheat germ agglutinin, a known inhibitor of nuclear pore-mediated transport. At least one target for trans-acting factors that promote nuclear export of SRP RNA appears to be the Alu element of the molecule, since a transcript consisting of only the Alu sequence was exported from the nucleus in a temperature-dependent manner and the Alu transcript competed in the nucleus for transport with intact SRP RNA. Although the identities of trans-acting factors responsible for SRP RNA transport are at present unknown, we suggest that proteins contained within the cytoplasmic form of SRP are candidates. Consistent with this idea were the effects of a mutation in SRP RNA that prevented binding of two known SRP proteins to the Alu sequence.
信号识别颗粒是一种细胞质RNA-蛋白质复合物，它介导分泌性多肽转运到内质网中。我们利用非洲爪蟾卵母细胞显微注射试验来确定信号识别颗粒（SRP）RNA是如何从细胞核输出的。核内注射后，SRP RNA在细胞质中积累，而细胞质注射的SRP RNA则不进入细胞核。SRP RNA在细胞质中的积累显然是一个依赖于有限反式作用因子的促进过程，因为核输出表现出饱和动力学，并且在低温或通过麦胚凝集素（一种已知的核孔介导转运的抑制剂）时完全被阻断。促进SRP RNA核输出的反式作用因子的至少一个靶点似乎是该分子的Alu元件，因为仅由Alu序列组成的转录本以温度依赖的方式从细胞核输出，并且Alu转录本在细胞核中与完整的SRP RNA竞争转运。尽管目前负责SRP RNA转运的反式作用因子的身份尚不清楚，但我们认为SRP细胞质形式中包含的蛋白质是候选者。与这一观点一致的是，SRP RNA中的一个突变阻止了两种已知的SRP蛋白与Alu序列结合的效应。
