tRNAs and proteins are imported into mitochondria of Trypanosoma brucei bytwo distinct mechanisms

Import of tRNA into the mitochondrial matrix of Trypanosoma brucei was reco nstituted in vitro. Efficient import required the hydrolysis of externally added ATP and was shown to be a carrier-mediated process depending on prote inaceous receptors on the surface of mitochondria. A partly synthetic tRNA( Tyr) as well as a physiological tRNA(Lys) were imported along the same path way. Contrary to import of all matrix-localized proteins, tRNA import does not require a membrane potential. Furthermore, addition of an excess of imp ort-competent tRNA had no effect on import of a mitochondrial matrix protei n. In summary, these results show that tRNAs and proteins in T. brucei are imported by fundamentally different mechanisms.