Evolutionary and functional aspects of C-to-U editing at position 28 of tRNACys(GCA) in plant mitochondria

In plant mitochondria, editing of messenger RNA by C-to-U conversions is essential for correct gene expression as it usually improves the protein-sequence conservation between different species or sometimes affects the reading frames (for a review, see Maier et al., 1996). Editing sites have been identified in mitochondrial (mt) RNA of all major groups of land plants, including Bryophytes, Pteridophytes, Prespermaphytes, and Spermaphytes (Hiesel et al., 1994a,b; Malek et al., 1996). Editing mainly affects messenger RNA, but editing sites have also been identified in three transfer RNAs. In dicot mitochondria a C-to-U editing event corrects a C:A mismatch into a U:A base pair in the acceptor stem of tRNAPhe(GAA) (Maréchal-Drouard et al., 1993; Binder et al., 1994). In the gymnosperm Larix leptoeuropaea, three C-to-U conversions restore a U:A base pair in the acceptor stem, D stem, and anticodon stem of tRNAHis(GUG), respectively (Maréchal-Drouard et al., 1996b). The third example described is the Oenothera berteriana mt tRNACys(GCA), where a C28:U42 mismatch is converted into a U28:U42 noncanonical base pair (Binder et al., 1994). In the case of both tRNAPhe and tRNAHis, editing of precursors is a prerequisite for 5′ and 3′ processing to generate a mature tRNA (Marchfelder et al., 1996; Maréchal-Drouard et al., 1996a, 1996b; Kunzmann et al., 1998). The role of editing in the case of tRNACys has not been studied so far, although it has been shown that it occurs at the precursor level (Binder et al., 1994). In this letter, we report an evolutionary and functional study of mt tRNACys(GCA) editing in plant mitochondria