酵母菌Saccharomyces cerevisiae中cytoplasmic glutamyl-tRNA synthetase (cGluRS) 是由細胞核基因GUS1解碼而來。在細胞質中cGluRS會將Glu接到相對應的tRNAGlu形成Glu-tRNAGlu，但是最近的研究報告指出cGluRS也會被送到粒腺體中參與Gln-tRNAGln的形成。在粒腺體中cGluRS首先會將Glu接到tRNAGln形成Glu-tNRAGln，再藉由Glu-tNRAGln amidotransferase的轉胺作用形成正確的Gln-tRNAGln。先前，我們實驗室指出，在細胞質中與cGluRS結合的分子Arc1p有粒腺體標的訊號，因此cGluRS有可能是藉由Arc1p而進入粒腺體的，經由點突變的實驗我們發現cGluRS和Arc1p各自攜帶粒腺體標的訊號，不需靠彼此交互作用而進入粒腺體。cGluRS的粒腺體標的訊號位於其胺基端1-29胺基酸。相反地，在酵母菌Schizosaccharomyces pombe及Candida albicans的cGluRS中並沒有發現類似的粒腺體標的訊號。而在Pichia guilliermodii、Candida albicans、Schizosaccharomyces pombe這三株酵母菌的Arc1p也沒有粒腺體標的訊號。 In Saccharomyces cerevisiae, the cytoplasmic glutamyl-tRNA synthetase (cGluRS) is encoded by GUS1. In cytoplasm, cGluRS attaches Glu to the cognate tRNAGlu to form Glu-tRNAGlu. In addition to the cytoplasmic activity, cGluRS can enter the mitochodria to synthesize Glu-tNRAGln (a misacylated product), which is then converted to correct Gln-tRNAGln by Glu-tNRAGln amidotransferase. A pervious study in our lab indicated that Arc1p, which binds cGluRS in cytoplasm, also has a mitochondrial targeting signal. Our results showed that cGluRS and Arc1p each carry a mitochondrial targeting signal and thus can enter the mitochondria by itself. Next, we used the cytoplasmic form of valyl-tRNA synthetase as the reporter gene to map the mitochondrial targeting signal of cGluRS. As it turned out, this signal was embedded in the N-terminal amino acids 1-29 of cGluRS. In contrast, no mitochondrial targeting signal was found in Schizosaccharomyces pombe or Candida albicans GluRS. Moreover, Arc1p from Pichia guilliermodii, Candida albicans, and Schizosaccharomyces pombe does not possess a mitochondrial targeting signal.
