15 RNA Editing: New Uses for Old Players in the RNA World

Abstract

The sequence of a cellular RNA cannot always be inferred from the gene that encodes it. Subsequent to transcription, certain RNAs are edited. RNA editing can involve the insertion or deletion of nucleotides, as well as the modification of encoded nucleotides. RNA editing is required in certain mRNAs to create initiation and termination codons, as well as to eliminate internal frameshifts and change the identity of internal amino acids. Recently, RNA editing has also been observed in certain tRNAs and rRNAs; here the edited residues appear to be necessary to maintain the three-dimensional structure that is crucial to the function of these RNAs.

At present, RNA editing has only been observed in eukaryotes, but in this kingdom it is widespread and found in mitochondrion-encoded RNAs of kinetoplastids, slime molds, and plants; chloroplast-encoded RNAs of plants; and nucleus-encoded RNAs of mammals (Table 1). Although once thought to be limited to the insertion and deletion of uridine residues, editing reactions that produce non-encoded adenosines, guanosines, cytidines, and possibly inosines, have now been described.

The discovery of each new example of editing begins with the observation that a genomic sequence does not correlate with the corresponding cDNA sequence. The discovery of so many examples of RNA editing in recent years is the result of technological advances in sequencing and the polymerase chain reaction (PCR). This review does not focus on the methodology behind the identification of edited transcripts, but rather on the subsequent studies performed to elucidate the mechanisms involved in the editing...