| Summary: | 碩士 === 國立中央大學 === 生命科學研究所 === 100 === In yeast, there are two distinct sets of aminoacyl-tRNA synthetases (aaRSs), one localized in the cytoplasm and the other in mitochondria. Paradoxically, there is only one histidyl-tRNA synthetase (HisRS) gene, HTS1, in the yeast nuclear genome. As it turns out, this gene encodes both cytoplasmic and mitochondrial forms of HisRS through alternative initiation of translation from two in-frame initiator codons. We herein report that a dual-functional phenotype was conserved in the HTS1 genes of other yeast species. While E. coli tRNAHis species contained a G-1:C73 base pair as the major determinant, yeast cytosolic and mitochondrial tRNAHis isoacceptors respectively contained G-1:A73 and G-1:C73 at the same position. Even though E. coli HisRS failed to substitute for the cytoplasmic activity of yeast HTS1, the bacterial enzyme, upon being imported into mitochondria, could rescue growth defect of a S. cerevisiae HTS1 knockout strain. In addition, we found that the N-terminal appended domain of S. cerevisiae HisRS and an insertion domain of L. elogisporous HisRS significantly contributed to KM of the enzyme for tRNAHis, but had relatively minor effect on the kcat. Our study suggests that the appended domain or insertion domain of yeast HisRS acts as an auxiliary tRNA-binding domain to improve the overall tRNA-binding affinity of the enzyme.
|
|---|
