Nucleic Acids Research, Vol 24, Issue 7 1225-1228, Copyright © 1996 by Oxford University Press
A Schneider
The mitochondrial genome of Trypanosoma brucei does not encode any tRNAs.
Instead, mitochondrial tRNAs are synthesized in the nucleus and
subsequently imported into mitochondria. The great majority of
mitochondrial tRNAs have cytosolic counterparts showing identical primary
sequences. The only difference found between mitochondrial and cytosolic
isotypes of the tRNAs are mitochondria-specific nucleotide modifications
which appear to be a common feature of imported tRNAs in trypanosomes. In
this study, a mutated yeast cytosolic tRNAHis was expressed in trypanosomes
and its import phenotype was analyzed by cell fractionation and nuclease
treatment of intact mitochondria. Furthermore, cytosolic and mitochondrial
isotypes of the yeast tRNA(His) were specifically labeled and analyzed by
limited alkaline hydrolysis. These experiments revealed the presence of
mitochondria- specific nucleotide modifications in the yeast tRNA(His). The
positions of the modifications were determined by direct enzymatic
sequencing of the tRNA(His) and shown to correspond to the ultimate and
penultimate nucleotides before the anticodon, the same relative positions
which are modified in the mitochondrial isotype of trypanosomal tRNA(Tyr).
The results demonstrate that covalent modification of tRNAs; in
trypanosomal mitochondria can be used, in analogy to processing of
precursor proteins during mitochondrial protein import, as a marker for
import of both endogenous and heterologous tRNAs.
ARTICLES
Cytosolic yeast tRNA(His) is covalently modified when imported into mitochondria of Trypanosoma brucei
Biozentrum, University of Basel, Department of Biochemistry, Switzerland.
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