Editing and Modification of Messenger RNA

Abstract

The discovery of messenger RNA (mRNA) more than 30 years ago led to the proposition of the central dogma of molecular biology that DNA makes RNA, and that RNA makes protein. Research has since shown that mRNA takes part in various complex reactions and is subject to a variety of co- and post-transcriptional modifications. RNA can be faithfully copied by reverse transcriptase, edited by the splicing out of intervening sequences, modified by capping and polyadenylation, and can itself catalyze transesterification reactions. None of these discoveries seriously challenges the central dogma of molecular biology. It came therefore as a considerable surprise to find that genetic information not found in the genomic template can be transferred into the mRNA after transcription. Thus, certain trypanosome mitochondrial mRNAs, which are unable to be translated for lack of AUG initiation codons or because of the presence of frameshifts in the coding sequence, are rendered translatable by the introduction or deletion of U residues that are not encoded in the mitochondrial or nuclear genome (Benne et al. 1986; Feagin et al. 1987, 1988; Abraham et al. 1988). Other modifications that alter the coding ability of mRNAs have since been discovered. These include the modification of apolipoprotein (apo)-B mRNA (Chen et al. 1987; Powell et al. 1987) and of plant mitochondrial mRNAs (Covello and Gray 1989; Gualberto et al. 1989; Hiesel et al., in press), in which C to U substitution occurs, and the addition of a nontemplated G residues, which shift the reading frame of paramyxovirus mRNAs (Thomas et al. 1988; Cattaneo et al. 1989; Paterson et al. 1989).