Unusual noncanonical intron editing is important for tRNA splicing in Trypanosoma brucei.

In cells, tRNAs are synthesized as precursor molecules bearing extra sequences at their 5′ and 3′ ends. Some tRNAs also contain introns which, in archaea and eukaryotes, are cleaved by an evolutionarily conserved endonuclease complex that generates fully functional mature tRNAs. In addition, tRNAs undergo numerous post-transcriptional nucleotide chemical modifications. In Trypanosoma brucei the single intron-containing tRNA (tRNATyrGUA) is responsible for decoding all tyrosine codons; therefore, intron removal is essential for viability. We show by molecular and biochemical approaches the presence of several non-canonical editing events, within the intron of pre-tRNATyrGUA, involving guanosine to adenosine transitions (G to A) and an adenosine to uridine transversion (A to U). The RNA editing described here is required for proper processing of the intron, establishing for the first time the functional significance of non-canonical editing with implications for tRNA processing in the deeply divergent kinetoplastid lineage and eukaryotes in general.

在细胞中，tRNA是以在前体分子形式合成的，其5′端和3′端带有额外的序列。一些tRNA还含有内含子，在古菌和真核生物中，这些内含子由一种进化上保守的内切核酸酶复合物切割，从而产生具有完全功能的成熟tRNA。此外，tRNA会经历大量转录后核苷酸化学修饰。在布氏锥虫中，唯一含内含子的tRNA（tRNATyrGUA）负责解码所有酪氨酸密码子；因此，内含子的去除对生存能力至关重要。我们通过分子和生化方法表明，在pre - tRNATyrGUA的内含子中存在几种非规范编辑事件，包括鸟苷到腺苷的转变（G到A）以及腺苷到尿苷的颠换（A到U）。此处描述的RNA编辑对于内含子的正确加工是必需的，首次确立了非规范编辑的功能重要性，这对差异极大的动基体目谱系以及一般的真核生物的tRNA加工具有启示意义。