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J. Biol. Chem., Vol. 279, Issue 41, 42363-42368, October 8, 2004

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Mitochondrial tRNA Import in Toxoplasma gondii^*

Anne Crausaz Esseiva, Arunasalam Naguleswaran, Andrew Hemphill, and André Schneider¶

From the Department of Biology/Zoology, University of Fribourg, Chemin du Musée 10, CH-1700 Fribourg and the Institute of Parasitology, University of Bern, Laenggass-Strasse 122, 3012 Bern, Switzerland

Apicomplexan parasites have the smallest known mitochondrial genome. It consists of a repeated element of 6–7 kb in length and encodes three mitochondrial proteins, a number of rRNA fragments, but no tRNAs. It has therefore been postulated that in apicomplexans all tRNAs required for mitochondrial translation are imported from the cytosol. To provide direct evidence for this process we have established a cell fractionation procedure allowing the isolation of defined organellar RNA fractions from the apicomplexan Toxoplasma gondii. Analysis of T. gondii total and organellar RNA by Northern hybridization showed that except for the cytosol-specific initiator tRNA^Met all nucleus-encoded tRNAs tested were present in the cytosol and in the mitochondrion but not in the plastid. Thus, these results provide the first experimental evidence for mitochondrial tRNA import in apicomplexans. The only other taxon that imports the whole set of mitochondrial tRNAs are the trypanosomatids. Interestingly, the initiator tRNA^Met is the only cytosol-specific tRNA in trypanosomatids, indicating that the import specificity is identical in both groups. In agreement with this, the T. gondii initiator tRNA^Met remained in the cytosol when expressed in Trypanosoma brucei. However, in contrast to trypanosomatids, no thio-modifications were detected in the tRNA^Gln of T. gondii indicating that, unlike what is suggested in Leishmania, they are not involved in regulating import.

Received for publication, April 23, 2004 , and in revised form, July 15, 2004.

^* This study was supported by Grants 31-067906.02 (to A. S.) and 32-067782.02 (to A. H.) from the Swiss National Foundation. Genomic data were provided by The Institute for Genomic Research (supported by National Institutes of Health (NIH) Grant AI05093), and by the Sanger Center (Wellcome Trust). Expressed Sequence Tag sequences were generated by Washington University (NIH Grant 1R01AI04580601A1). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

^¶ To whom correspondence should be addressed. Tel.: 41-26-300-8877; Fax: 41-26-300-9741; E-mail: andre.schneider{at}unifr.ch.

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