Rusconi C P, Cech T R
Department of Molecular, Cellular, and Developmental Biology, Howard Hughes Medical Institute, University of Colorado, Boulder 80309-0215, USA.
Genes Dev. 1996 Nov 15;10(22):2870-80. doi: 10.1101/gad.10.22.2870.
The import of nuclear-encoded RNAs into mitochondria is required for proper mitochondrial function in most organisms. However, the mechanisms used to achieve RNA import are largely unknown. In particular, the RNA elements that direct import have not been identified in any organism. In Tetrahymena, only one of three nuclear-encoded glutamine accepting tRNAs is imported into mitochondria. We transform Tetrahymena with marked glutamine tRNAs and quantitate their level of accumulation in mitochondria. Of several isostructural nucleotide substitutions tested, alteration of the anticodon sequence uniquely abolishes import. Furthermore, substitution of a single anticodon nucleotide (UUA-->UUG) confers import on a normally nonimported glutamine tRNA. Thus, the anticodon functions as a mitochondrial localization signal and is both necessary and sufficient for tRNA import. Given the prior evidence that neither the cytoplasmic nor the mitochondrial glutaminyl-tRNA synthetase distinguishes between the imported and nonimported glutamine tRNAs with respect to aminoacylation, we propose that some mitochondrial import factor distinct from a synthetase recognizes the anticodon of the imported glutamine tRNA.
在大多数生物体中，将核编码的RNA导入线粒体是线粒体正常功能所必需的。然而，实现RNA导入的机制在很大程度上尚不清楚。特别是，在任何生物体中都尚未鉴定出指导导入的RNA元件。在四膜虫中，三个核编码的谷氨酰胺接受tRNA中只有一个被导入线粒体。我们用标记的谷氨酰胺tRNA转化四膜虫，并定量它们在线粒体中的积累水平。在测试的几种同结构核苷酸替代中，反密码子序列的改变独特地消除了导入。此外，单个反密码子核苷酸的替代（UUA→UUG）赋予了一种通常不被导入的谷氨酰胺tRNA导入能力。因此，反密码子作为线粒体定位信号，对于tRNA导入既是必要的也是充分的。鉴于先前的证据表明，细胞质和线粒体谷氨酰胺tRNA合成酶在氨基酰化方面都不能区分导入的和未导入的谷氨酰胺tRNA，我们提出一些不同于合成酶的线粒体导入因子识别导入的谷氨酰胺tRNA的反密码子。
