Editing in plant mi to chon dria con sists in C to U changes and mainly af fects mes senger RNAs, thus pro vid ing the cor rect ge netic in for ma tion for the biosynthesis of mi to- chon drial (mt) pro teins. But ed it ing can also af fect some of the plant mt tRNAs encoded by the mt ge nome. In di cots, a C to U ed it ing event cor rects aC:A mis match into a U:A base-pair in the acceptor stem of mt tRNAPhe (GAA). In larch mitochondria, three C to U ed it ing events re store U: A base-pairs in the ac cep tor stem, D stem and anticodon stem, re spec tively, of mt tRNAHis (GUG). For both these mt tRNAs ed it ing of the pre cur sors is a pre req ui site for their pro cess ing into ma ture tRNAs. In po tato mt tRNACys (GCA), ed it ing con verts a C28:U42 mis match in the anticodon stem into a U28:U42 non-canonical base-pair, and reverse transcriptase minisequencing has shown that the mature mt tRNACys is fully edited. In the bryophyte Marchantia polymorpha this U res i due is en coded in the mt ge nome and evo lu tion ary stud ies sug gest that res to ra tion of the U28 res i due is nec es sary when it is not en coded in the gene. How ever, in vitro stud ies have shown that nei ther pro cess- ing of the pre cur sor nor amino acylation of tRNACys re quires C to U ed it ing at this po- si tion. But se quenc ing of the pu ri fied mt tRNACys has shown that Y is pres ent at po si tion 28, indicating that C to U editing is a prerequisite for the subsequent isomerization of U into Y at po si tion 28.
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