Rubio Mary Anne T, Pastar Irena, Gaston Kirk W, Ragone Frank L, Janzen Christian J, Cross George A M, Papavasiliou F Nina, Alfonzo Juan D
Department of Microbiology and the Ohio State RNA Group, Ohio State University, Columbus, OH 43210, USA.
Proc Natl Acad Sci U S A. 2007 May 8;104(19):7821-6. doi: 10.1073/pnas.0702394104. Epub 2007 May 1.
Adenosine-to-inosine editing in the anticodon of tRNAs is essential for viability. Enzymes mediating tRNA adenosine deamination in bacteria and yeast contain cytidine deaminase-conserved motifs, suggesting an evolutionary link between the two reactions. In trypanosomatids, tRNAs undergo both cytidine-to-uridine and adenosine-to-inosine editing, but the relationship between the two reactions is unclear. Here we show that down-regulation of the Trypanosoma brucei tRNA-editing enzyme by RNAi leads to a reduction in both C-to-U and A-to-I editing of tRNA in vivo. Surprisingly, in vitro, this enzyme can mediate A-to-I editing of tRNA and C-to-U deamination of ssDNA but not both in either substrate. The ability to use both DNA and RNA provides a model for a multispecificity editing enzyme. Notably, the ability of a single enzyme to perform two different deamination reactions also suggests that this enzyme still maintains specificities that would have been found in the ancestor deaminase, providing a first line of evidence for the evolution of editing deaminases.
转运RNA（tRNA）反密码子中的腺苷到次黄苷编辑对于细胞存活至关重要。介导细菌和酵母中tRNA腺苷脱氨的酶含有胞苷脱氨酶保守基序，这表明这两种反应之间存在进化联系。在锥虫中，tRNA经历胞苷到尿苷和腺苷到次黄苷的编辑，但这两种反应之间的关系尚不清楚。在这里，我们表明通过RNA干扰下调布氏锥虫tRNA编辑酶会导致体内tRNA的C到U和A到I编辑均减少。令人惊讶的是，在体外，这种酶可以介导tRNA的A到I编辑和单链DNA的C到U脱氨，但不能在任何一种底物中同时介导这两种反应。使用DNA和RNA的能力为多特异性编辑酶提供了一个模型。值得注意的是，单一酶执行两种不同脱氨反应的能力也表明该酶仍然保持着在祖先脱氨酶中发现的特异性，为编辑脱氨酶的进化提供了首个证据。
