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

酵母半胱氨酸脱硫酶Nfs1p缺陷导致线粒体(mt-)tRNAs和胞浆(Cy-)tRNAs尿苷2-硫基修饰严重受损。NFS1p还可以提供线粒体和胞质Fe/S团簇组装机制产生的铁硫(Fe/S)团簇的硫原子，分别称为ISC和CIA。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室tRNAs 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以外的线粒体ISC和/或胞质CIA组分是否参与这些tRNA的2-硫代修饰。我们在这里证明了Cy-tRNAs的2-thio修饰需要三个CIA成分，Cfd1p、Nbp35p和Cia1p，而mt-tRNAs不需要。有趣的是，线粒体支架蛋白lsu1p和Isu2p是胞质tRNA的2-thio修饰所必需的，而线粒体tRNAs的2-thio修饰不需要线粒体Nfs1p。这些结果清楚地表明，胞质tRNA的2-thio修饰是铁/S蛋白依赖的，因此需要CIA和ISC两种机制，而线粒体tRNA的2-thio修饰是Fe/S簇无关的，除了Nfs1p外不需要线粒体ISC的关键成分。

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.