RRM
2007 Rustbelt RNA Meeting
RRM
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Poster abstracts
Abstract:
In Leishmania and Trypanosoma species, tRNAs are transcribed in the nucleus and imported from the cytosol into the mitochondrion. The only tRNATrp encoded within the nucleus of these organisms contains a CCA anticodon that can decode the UGG codon in the cytosol, but is unable to decode the UGA tryptophan codons in mitochondria. Trypanosomatids have solved this problem of UGA decoding by specifically changing the first position of the anticodon of tRNATrpCCA from cytidine (C34) to uridine (U34) by RNA editing, following import into the mitochondrion. In addition, this tRNA undergoes a number of posttranscriptional chemical modifications in the anticodon stem loop following mitochondrial import. Notably, position 33 (adjacent to the edited nucleotide) becomes thiolated but only in the edited tRNA species. We have hypothesized that thiolation of the normally unmodified U33 (97% of all the sequenced tRNAs from various organisms have an unmodified U33) to be an essential prerequisite for C to U editing of tRNATrp in trypanosomatids and thus important for cell viability. In E. coli, formation of s2U in tRNA is mediated by the cysteine desulfurase, IscS. In Trypanosoma brucei there are two IscS homologs, a cytosolic protein and a protein targeted to the mitochondria. Here we show by using RNAi that the mitochondria-targeted IscS is responsible for s2U formation in both cytosolic and mitochondrial tRNAs. Since thiolation of tRNAs may play a critical role in both tRNA editing and import into the mitochondria, further studies should shed light into how this modification may regulate both processes.
Keywords: RNA, Modification
