title: Thiolated tRNAs of Trypanosoma brucei are imported into mitochondria and dethiolated after import.
abstract: All mitochondrial tRNAs in Trypanosoma brucei derive from cytosolic tRNAs that are in part imported into mitochondria. Some trypanosomal tRNAs are thiolated in a compartment-specific manner. We have identified three proteins required for the thio modification of cytosolic tRNA(Gln), tRNA(Glu), and tRNA(Lys). RNA interference-mediated ablation of these proteins results in the cytosolic accumulation non-thio-modified tRNAs but does not increase their import. Moreover, in vitro import experiments showed that both thio-modified and non-thio-modified tRNA(Glu) can efficiently be imported into mitochondria. These results indicate that unlike previously suggested the cytosol-specific thio modifications do not function as antideterminants for mitochondrial tRNA import. Consistent with these results we showed by using inducible expression of a tagged tRNA(Glu) that it is mainly the thiolated form that is imported in vivo. Unexpectedly, the imported tRNA becomes dethiolated after import, which explains why the non-thiolated form is enriched in mitochondria. Finally, we have identified two genes required for thiolation of imported tRNA(Trp) whose wobble nucleotide is subject to mitochondrial C to U editing. Interestingly, down-regulation of thiolation resulted in an increase of edited tRNA(Trp) but did not affect growth.
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland.
authors.forename: Ellen Inga
authors.initials: EI
authors.lastname: Bruske
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland.
authors.forename: Franziska
authors.initials: F
authors.lastname: Sendfeld
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland. Electronic address: andre.schneider@ibc.unibe.ch.
authors.forename: André
authors.initials: A
authors.lastname: Schneider
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D012323:RNA Processing, Post-Transcriptional / Q000502:physiology*; D016053:RNA, Protozoan / Q000235:genetics / Q000378:metabolism*; D012343:RNA, Transfer / Q000235:genetics / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000378:metabolism*; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000378:metabolism*
chemical_list: D016053:RNA, Protozoan; D013438:Sulfhydryl Compounds; D012343:RNA, Transfer