Tarassov I A, Martin R P
UPR 9005 MMDCD, CNRS, Strasbourg, France.
Biochimie. 1996;78(6):502-10. doi: 10.1016/0300-9084(96)84756-0.
Mitochondrial import of tRNA is now considered as a quasi-universal phenomenon. In the yeast Saccharomyces cerevisiae, one of the three lysine isoacceptors, the tRNA(Lys)1 with the anticodon CUU (tRNA-K1), is encoded by the nuclear genome and distributed between the cytoplasmic (> 95%) and mitochondrial (< 5%) compartments. In vivo and in vitro import assays were developed to study the mechanisms of tRNA-K1 mitochondrial import. Transmembrane translocation of the tRNA requires the intactness of at least two of the components of the mitochondrial import machinery of pre-proteins, MOM19 and MIM44, as well as energy of ATP hydrolysis and an electrochemical potential across the inner membrane. The import of tRNA-K1 involves formation of an RNP complex on the mitochondrial outer membrane. tRNA-K1 import is also dependent upon cytosolic protein factors, one of which was identified as the precursor of the mitochondrial lysyl-tRNA synthetase (MSK). Although essential for tRNA-K1 import in vitro and in vivo, pre-MSK is however not sufficient to direct the import in vitro, which suggests the need of additional cytosolic factor(s). The tRNA can be imported in its mature form and nucleoside modification is not essential. Aminoacylation of the imported tRNA by the cytoplasmic lysyl-tRNA synthetase is a prerequisite for import. Possible mechanisms of intracellular partitioning and mitochondrial membrane translocation of tRNA-K1 are discussed.
如今，tRNA的线粒体导入被认为是一种近乎普遍的现象。在酿酒酵母中，三种赖氨酸同工受体之一、反密码子为CUU的tRNA（Lys）1（tRNA-K1）由核基因组编码，并分布于细胞质（>95%）和线粒体（<5%）区室之间。已开发出体内和体外导入试验来研究tRNA-K1线粒体导入的机制。tRNA的跨膜转运需要前体蛋白线粒体导入机制的至少两个组分（MOM19和MIM44）保持完整，以及ATP水解的能量和内膜上的电化学势。tRNA-K1的导入涉及在线粒体外膜上形成RNP复合物。tRNA-K1的导入还依赖于胞质蛋白因子，其中一种被鉴定为线粒体赖氨酰-tRNA合成酶（MSK）的前体。尽管前体MSK在体内和体外对tRNA-K1的导入都是必需的，但它在体外并不足以指导导入，这表明还需要其他胞质因子。tRNA可以以其成熟形式导入，核苷修饰并非必需。由胞质赖氨酰-tRNA合成酶对导入的tRNA进行氨酰化是导入的前提条件。文中讨论了tRNA-K1在细胞内分配和线粒体膜转运的可能机制。
