經過數十年探索，對於aminoacyl-tRNA synthetases (aaRSs)的功能以及結構的理解已有長足進展。相較之下，對於他們的演化路徑仍然相當模糊，尤其是具有雙重功能之基因，例如valyl-tRNA synthetase (ValRS)。因此，在此我們著眼於酵母菌ValRS 的演化情形及其附加區段的功能。過去的研究指出酵母基因VAS1可轉譯出細胞質以及粒線體的ValRS。我們發現大腸桿菌 ValRS基因無法取代酵母菌VAS1基因的功能。但是，藉由將其與酵母菌ValRS附加區段或其它非專一性的tRNA 鍵結區段(TRBD)以及粒線體標的訊號(MTS)結合，能將E. coli ValRS轉變成一個雙功能的酵母菌ValRS。而除了裂殖酵母菌Schizosaccharomyces pombe之外，其它的酵母菌都只具有一個ValRS基因。S. pombe有兩個位於染色體的同源基因 SpVAS1和SpVAS2，分別執行細胞質和線粒體功能。令人驚訝的是他們都是源自粒線體的基因，這表示真核生物ValRS的演化並不是單純地由內共生和線粒,體基因轉移到細胞核而形成的。除此之外，我們發現了S. pombe的tRNA結合蛋白Asc1p與核醣體有交互作用。此研究不僅提出一個ValRS如何由原核生物演化成現代酵母菌的概念，也顯示 Asc1p以及ValRS之附加區段可能與aminoacyl-tRNA 之傳輸有關。 After decades of exploration, knowledge of structure and functions of aminoacyl-tRNA synthetases (aaRSs) has progressed by leaps and bounds. However, their evolution paths are still obscure, especially for the dual-functional genes such as valyl-tRNA synthetase (ValRS). We focus herein on the evolution of yeast ValRS and its appended domain. Previous studies showed a single yeast gene, VAS1, encodes both cytosolic and mitochondrial forms of ValRS. We show that ValRS of Escherichia coli per se cannot substitute for yeast ValRS, but can be converted into a dual-functional yeast enzyme by fusion to the appended domain of yeast ValRS or a nonspecific tRNA-binding domain (TRBD) and a mitochondrial targeting signal (MTS). Interestingly, except for the fission yeast Schizosaccharomyces pombe, all yeast species studied contained a single ValRS gene. There are two homologous ValRS genes in the chromosomes of S. pombe, named SpVAS1 and SpVAS2, which specify cytosolic and mitochondrial functions, respectively. Surprisingly, both of them are of mitochondria origin. This finding suggests that evolution of eukaryotic ValRS invloved processes more than endosymbiosis and mitochondria-to-nucleus gene transfer. In addition, we found that the tRNA-binding protein Asc1p of S. pombe associates with ribosomal proteins. These findings not only suggest an evolutionary path for ValRS from prokaryotes to modern yeasts, but also underscore the possibility that both the appended domain of yeast ValRS and Asc1p play a role in aminoacyl-tRNA channeling.
