Thiolated tRNAs of Trypanosoma brucei Are Imported into Mitochondria and Dethiolated after Import*

  1. André Schneider1
  1. From the Department of Chemistry and Biochemistry, University of Bern, Freiestrasse 3, CH-3012 Bern, Switzerland
  1. 1 To whom correspondence should be addressed. Tel.: 0041-31-6314253; Fax: 0041-31-631-4887; E-mail: andre.schneider{at}ibc.unibe.ch.

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 tRNAGln, tRNAGlu, and tRNALys. 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 tRNAGlu 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 tRNAGlu 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 tRNATrp whose wobble nucleotide is subject to mitochondrial C to U editing. Interestingly, down-regulation of thiolation resulted in an increase of edited tRNATrp but did not affect growth.

Footnotes

  • * This work was supported by Grant 3100A0_121937 (to A. S.) from the Swiss National Foundation.

  • Received September 9, 2009.
  • Revision received October 15, 2009.
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This Article

  1. The Journal of Biological Chemistry 284, 36491-36499.
  1. All Versions of this Article:
    1. M109.064527v1
    2. 284/52/36491 (most recent)

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