In vivo, yeast mitochondria import a single cytoplasmic tRNA, tRNA(CUU)Lys, while human mitochondria do not import any cytoplasmic tRNA. We have previously demonstrated that both yeast and human isolated mitochondria can specifically internalize tRNA(CUU)Lys, several of its mutant versions and some mutant versions of yeast cytosolic tRNA(UUU)Lys (not imported in vivo). Aminoacylation of tRNA(CUU)Lys by the cytoplasmic lysyl-tRNA synthetase was a prerequisite for its import. Here we are studying the influence of one-base replacements in the anticodon of tRNAs(Lys) on their aminoacylation, on binding to the precursor of the mitochondrial lysyl-tRNA synthetase (carrier protein directing the import), and on the efficiency of import into isolated yeast and human mitochondria. We show that the base U35 is the main identity element for the yeast cytoplasmic lysyl-tRNA synthetase. The single replacement that abolished import was C34G, while all the others only modulated the import efficiency. The need of aminoacylation for import and for interaction with the carrier protein was shown only for a subset of mutant versions, while the others could be recognized and internalized without aminoacylation or in misacylated forms.

中文翻译：

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tRNA 靶向酵母和人类线粒体：反密码子核苷酸的作用

在体内，酵母线粒体导入单个细胞质 tRNA，tRNA(CUU)Lys，而人类线粒体不导入任何细胞质 tRNA。我们之前已经证明，酵母和人类分离的线粒体都可以特异性地内化 tRNA(CUU)Lys、它的几个突变版本和酵母细胞溶质 tRNA(UUU)Lys 的一些突变版本（未在体内导入）。细胞质赖氨酰-tRNA 合成酶对 tRNA(CUU)Lys 的氨基酰化是其导入的先决条件。在这里，我们正在研究 tRNA (Lys) 反密码子中的单碱基替换对其氨酰化、与线粒体赖氨酰-tRNA 合成酶（指导导入的载体蛋白）前体结合以及导入效率的影响分离酵母和人类线粒体。我们表明碱基 U35 是酵母细胞质赖氨酰-tRNA 合成酶的主要身份元素。取消进口的单一替代品是C34G，而所有其他替代品仅调节进口效率。仅对一部分突变体版本显示出需要氨酰化以导入和与载体蛋白相互作用，而其他突变体无需氨酰化或以异酰化形式即可被识别和内化。