title: Lack of tRNA-i6A modification causes mitochondrial-like metabolic deficiency in S. pombe by limiting activity of cytosolic tRNATyr, not mito-tRNA.
abstract: tRNA-isopentenyl transferases (IPTases) are highly conserved enzymes that form isopentenyl-N(6)-A37 (i6A37) on subsets of tRNAs, enhancing their translation activity. Nuclear-encoded IPTases modify select cytosolic (cy-) and mitochondrial (mt-) tRNAs. Mutation in human IPTase, TRIT1, causes disease phenotypes characteristic of mitochondrial translation deficiency due to mt-tRNA dysfunction. Deletion of the Schizosaccharomyces pombe IPTase (tit1-Δ) causes slow growth in glycerol, as well as in rapamycin, an inhibitor of TOR kinase that maintains metabolic homeostasis. Schizosaccharomyces pombe IPTase modifies three different cy-tRNAs(Ser) as well as cy-tRNA(Tyr), cy-tRNA(Trp), and mt-tRNA(Trp). We show that lower ATP levels in tit1-Δ relative to tit1(+) cells are also more decreased by an inhibitor of oxidative phosphorylation, indicative of mitochondrial dysfunction. Here we asked if the tit1-Δ phenotypes are due to hypomodification of cy-tRNA or mt-tRNA. A cytosol-specific IPTase that modifies cy-tRNA, but not mt-tRNA, fully rescues the tit1-Δ phenotypes. Moreover, overexpression of cy-tRNAs also rescues the phenotypes, and cy-tRNA(Tyr) alone substantially does so. Bioinformatics indicate that cy-tRNA(Tyr) is most limiting for codon demand in tit1-Δ cells and that the cytosolic mRNAs most loaded with Tyr codons encode carbon metabolilizing enzymes, many of which are known to localize to mitochondria. Thus, S. pombe i6A37 hypomodification-associated metabolic deficiency results from hypoactivity of cy-tRNA, mostly tRNA(Tyr), and unlike human TRIT1-deficiency does not impair mitochondrial translation due to mt-tRNA hypomodification. We discuss species-specific aspects of i6A37. Specifically relevant to mitochondria, we show that its hypermodified version, ms2i6A37 (2-methylthiolated), which occurs on certain mammalian mt-tRNAs (but not cy-tRNAs), is not found in yeast.
authors: Section on Molecular and Cell Biology, Intramural Research Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors: Tek N
authors: TN
authors: Lamichhane
authors: Section on Molecular and Cell Biology, Intramural Research Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors: Aneeshkumar G
authors: AG
authors: Arimbasseri
authors: Section on Molecular and Cell Biology, Intramural Research Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors: Keshab
authors: K
authors: Rijal
authors: Molecular Genetics Laboratory, Intramural Research Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors: James R
authors: JR
authors: Iben
authors: Department of Molecular Physiology, Faculty of Life Sciences, Kumamoto University, 860-0862 Kumamoto, Japan.
authors: Fan Yan
authors: FY
authors: Wei
authors: Department of Molecular Physiology, Faculty of Life Sciences, Kumamoto University, 860-0862 Kumamoto, Japan.
authors: Kazuhito
authors: K
authors: Tomizawa
authors: Section on Molecular and Cell Biology, Intramural Research Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA Commissioned Corps, US Public Health Service, Rockville, Maryland 20016, USA.
authors: Richard J
authors: RJ
authors: Maraia
mesh_terms: D000818:Animals; D003062:Codon; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D014176:Protein Biosynthesis; D012323:RNA Processing, Post-Transcriptional; D012331:RNA, Fungal / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012365:RNA, Transfer, Tyr / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics; D012568:Schizosaccharomyces / Q000235:genetics / Q000378:metabolism*
chemical_list: D003062:Codon; D012331:RNA, Fungal; D012333:RNA, Messenger; D012365:RNA, Transfer, Tyr
keywords: mitochondria