title: The 2-thiouridylase function of the human MTU1 (TRMU) enzyme is dispensable for mitochondrial translation.
abstract: MTU1 (TRMU) is a mitochondrial enzyme responsible for the 2-thiolation of the wobble U in tRNA(Lys), tRNA(Glu) and tRNA(Gln), a post-transcriptional modification believed to be important for accurate and efficient synthesis of the 13 respiratory chain subunits encoded by mtDNA. Mutations in MTU1 are associated with acute infantile liver failure, and this has been ascribed to a transient lack of cysteine, the sulfur donor for the thiouridylation reaction, resulting in a mitochondrial translation defect during early development. A mutation in tRNA(Lys) that causes myoclonic epilepsy with ragged-red fibers (MERRF) is also reported to prevent modification of the wobble U. Here we show that mitochondrial translation is unaffected in fibroblasts from an MTU1 patient, in which MTU1 is undetectable by immunoblotting, despite the severe reduction in the 2-thiolation of mitochondrial tRNA(Lys), tRNA(Glu) and tRNA(Gln). The only respiratory chain abnormality that we could observe in these cells was an accumulation of a Complex II assembly intermediate, which, however, did not affect the level of the fully assembled enzyme. The identical phenotype was observed by siRNA-mediated knockdown of MTU1 in HEK 293 cells. Further, the mitochondrial translation deficiencies present in myoblasts from mitochondrial encephalomyopathy, lactic acidosis and stroke-like episode and MERRF patients, which are associated with defects in post-transcriptional modification of mitochondrial tRNAs, did not worsen following knockdown of MTU1 in these cells. This study demonstrates that MTU1 is not required for mitochondrial translation at normal steady-state levels of tRNAs, and that it may possess an as yet uncharacterized function in another sulfur-trafficking pathway.
authors: Montreal Neurological Institute, McGill University, Montreal H3A 2B4, Canada.
authors: Florin
authors: F
authors: Sasarman
authors: Hana
authors: H
authors: Antonicka
authors: Rita
authors: R
authors: Horvath
authors: Eric A
authors: EA
authors: Shoubridge
mesh_terms: D004591:Electrophoresis, Polyacrylamide Gel; D005347:Fibroblasts / Q000201:enzymology / Q000473:pathology; D055785:Gene Knockdown Techniques; D057809:HEK293 Cells; D006801:Humans; D017241:MELAS Syndrome / Q000201:enzymology / Q000473:pathology; D017243:MERRF Syndrome / Q000201:enzymology / Q000473:pathology; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000172:deficiency / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D032446:Myoblasts / Q000201:enzymology / Q000473:pathology; D010085:Oxidative Phosphorylation; D014176:Protein Biosynthesis; D012343:RNA, Transfer / Q000378:metabolism; D013891:Thiouridine / Q000378:metabolism; D012359:tRNA Methyltransferases / Q000172:deficiency / Q000378:metabolism*
chemical_list: D024101:Mitochondrial Proteins; D013891:Thiouridine; D012343:RNA, Transfer; D012359:tRNA Methyltransferases; C496706:TRMU protein, human