A-to-I and C-to-U editing within transfer RNAs

A significant number of post-transcriptional changes occur during the generation of mature transfer RNAs (tRNAs). These changes within precursor-tRNA molecules include the processing of 5' and 3' termini, the introduction of modifications, and also RNA editing. In this review, we will detail the reported cases of A-to-I and C-to-U tRNA editing. The most widespread example is the A-to-I conversion of the tRNA anticodon wobble base mediated by TadA in prokaryotes and the heterodimeric ADAT2-ADAT3 complex in eukaryotes. Recently, the plant chloroplast adenosine-to-inosine tRNA editing enzyme has been discovered. The editing of C-to-U is much less prevalent within tRNA and is currently only known to occur in few organellar tRNA species and the cytoplasmic threonyl-tRNA in trypanosomatids. The responsible editing enzyme remains to be identified. Finally, an unusually widespread C-to-U editing scenario was discovered in the archaeon Methanopyrus kandleri. This editing is mediated by CDAT8, which is responsible for the restoration of the proper folding of thirty different tRNA species. The evolution of CDAT8 will be discussed.