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Zusammenfassung:
tRNAs play a critical role in mRNA decoding, and posttranscriptional
modifications within tRNAs drive decoding efficiency and accuracy. The
types and positions of tRNA modifications in model bacteria have been
extensively studied, and tRNA modifications in a few eukaryotic
organisms have also been characterized and localized to particular tRNA
sequences. However, far less is known regarding tRNA modifications in
archaea. While the identities of modifications have been determined for
multiple archaeal organisms, Haloferax volcanii is the only organism for
which modifications have been extensively localized to specific tRNA
sequences. To improve our understanding of archaeal tRNA modification
patterns and codondecoding strategies, we have used liquid
chromatography and tandem mass spectrometry to characterize and then map
posttranscriptional modifications on 34 of the 35 unique tRNA sequences
of Methanocaldococcus jannaschii. A new posttranscriptionally modified
nucleoside, 5-cyanomethyl-2-thiouridine (cnm(5)s(2)U), was discovered
and localized to position 34. Moreover, data consistent with wyosine
pathway modifications were obtained beyond the canonical tRNA(Phe) as is
typical for eukaryotes. The high-quality mapping of tRNA anticodon loops
enriches our understanding of archaeal tRNA modification profiles and
decoding strategies.
IMPORTANCE While many posttranscriptional modifications in M. jannaschii
tRNAs are also found in bacteria and eukaryotes, several that are unique
to archaea were identified. By RNA modification mapping, the
modification profiles of M. jannaschii tRNA anticodon loops were
characterized, allowing a comparative analysis with H. volcanii
modification profiles as well as a general comparison with bacterial and
eukaryotic decoding strategies. This general comparison reveals that M.
jannaschii, like H. volcanii, follows codon-decoding strategies similar
to those used by bacteria, although position 37 appears to be modified
to a greater extent than seen in H. volcanii.
