Thlo modification of yeast cytosolic tRNA is an iron-sulfur protein-dependent pathway

酵母半胱氨酸脱硫酶Nfs1p的缺陷导致线粒体（mt-） trna和细胞质（cy-） trna的尿苷2-硫代修饰严重受损。Nfs1 p还可以提供由线粒体和细胞质中分别称为ISC和CIA的铁硫（Fe/S）簇组装机制产生的铁硫（Fe/S）簇的硫原子。因此，一个关键的问题仍然是Fe/S簇的生物合成是否是酵母细胞两个亚细胞区室中trna的2-硫代修饰的先决条件。为了阐明这个问题，我们询问除了Nfs1p外，线粒体ISC和/或细胞质CIA成分是否参与这些trna的2-硫代修饰。我们在这里证明了三种CIA成分Cfd1p、Nbp35p和Cia1p是cy- trna的2硫代修饰所必需的，而不是mt- trna的2硫代修饰。有趣的是，线粒体支架蛋白lsu1p和Isu2p是胞质trna的2硫代修饰所必需的，而线粒体trna的2硫代修饰则不需要线粒体Nfs1p。这些结果清楚地表明，胞质trna的2-硫代修饰是Fe/S蛋白依赖的，因此需要CIA和ISC机制，而线粒体trna的2-硫代修饰是Fe/S簇独立的，不需要除Nfs1p外的关键线粒体ISC成分。

Defects in yeast cysteine desulfurase, Nfs1p cause a severe impairment in 2-thio modification of uridine of the mitochondrial (mt-) tRNAs and the cytosolic (cy-) tRNAs. Nfs1 p can also provide the sulfur atoms of the iron-sulfur (Fe/S) clusters generated by the mitochondrial and cytosolic Fe/S cluster assembly machineries termed ISC and CIA, respectively. Therefore, a key question remains as to whether biosynthesis of Fe/S clusters is a prerequisite for the 2-thio modification of tRNAs in both subcellular compartments of yeast cells. To elucidate this question, we asked if mitochondrial ISC and/or cytosolic CIA components except Nfs1p would be involved in 2-thio modification of these tRNAs. We demonstrate here that the three CIA components, Cfd1p, Nbp35p, and Cia1p, are required for the 2-thio modification of cy-tRNAs but not of mt-tRNAs. Interestingly, the mitochondrial scaffold proteins lsu1p and Isu2p are required to the 2-thio modification of the cytosolic tRNAs but not of the mitochondrial tRNAs while mitochondrial Nfs1p is required for both 2-thio modifications. These results clearly indicate that the 2-thio modification of cytosolic tRNAs is Fe/S protein-dependent and thus requires both CIA and ISC machineries but that of mitochondrial tRNAs is Fe/S cluster-independent and does not require key mitochondrial ISC components except Nfs1p.