Formation of Gln-tRNAGln in the yeast mitochondria

• Main Authors: Chih-chi Liao, 廖芝淇
• Other Authors: Chien-chia Wang
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/16691802464658973349

碩士 === 國立中央大學 === 生命科學研究所 === 99 === There are two pathways for Gln-tRNAGln formation in the cell, a direct pathway, which involves GlnRS, and an indirect pathway, which involves a GatFAB transamidase. In Saccharomyces cerevisiae, early research indicated that a portion of cytoplasmic GlnRS was transported into the mitochondria. It was thus proposed that the yeast mitochondria may employ a direct pathway to form Gln-tRNAGln. However, a recent study argued that an indirect pathway is actually involved in the synthesis of mitochondrial Gln-tRNAGln. As a result, the true biological function of the imported GlnRS in the mitochondria is still elusive. In this study, we used reporter gene assays, and immunofluorescence analysis to map the mitochondrial targeting signal of yeast GlnRS. Our results showed that the signal is located at an internal segment close to the active site of the enzyme. This might be one of few examples of mitochondrial matrix proteins that use an uncleavable internal sequence as the mitochondrial targeting signal. On the other hand, we found that fusion of Arc1p to EcGlnRS enables the bacterial enzyme to rescue the growth defect of a GLN4 knockout strain. Further fusion of a mitochondrial targeting signal to the fusion enzyme Arc1p-EcGlnRS enabled the enzyme to replace the indirect pathway for Gln-tRNAGln formation in the mitochondria. These findings underscore the possibility of a horizontal transfer event, where an indirect pathway for Gln-tRNAGln formation is substituted for by a direct pathway.