RNA Editing: Evolutionary Implications


The term ‘ribonucleic acid (RNA) editing’ describes a variety of mechanistically unrelated biochemical activities that alter RNA molecules after transcription by addition, deletion or substitution of nucleotides. Examples include insertion and deletion of uridine residues in the mitochondrial messenger RNAs (mRNAs) of kinetoplastid protozoa; cytidine‐to‐uridine deamination of specific residues in the mitochondrial mRNAs and transfer RNAs (tRNAs) of land plants; conversion of adenosine to inosine via deamination in the nuclear transcripts of metazoan animals; and replacement of nonbase‐paired nucleotides at the 5′ and 3′ ends of certain mitochondrial tRNAs. A three‐stage ‘constructive neutral evolution’ (CNE) model, illustrated by specific examples, can explain in a general way how RNA‐editing systems might arise and become fixed. The CNE model proposes that potential editing systems arise before there is an actual requirement for editing, thereby serving to relax functional constraints at the genome level because harmful/lethal mutations are able to be reversed at the level of the corresponding transcript.

Key Concepts:

  • RNA editing is a process (typically post‐transcriptional) that alters the nucleotide sequence of an RNA molecule relative to the corresponding gene sequence.

  • Two general types of RNA editing are recognised: (1) insertional, in which nucleotides are added to (and also deleted from) internal positions and (2) substitutional, in which one nucleotide type replaces another at particular positions.

  • All types of cellular RNA (messenger, transfer and ribosomal) may undergo editing, as well as intron, noncoding and viral sequences.

  • RNA‐editing systems are almost exclusively restricted to eukaryotes, and are especially prominent in chloroplasts and mitochondria.

  • RNA‐editing systems are clearly derived traits, arising relatively recently within particular eukaryotic lineages.

  • RNA‐editing systems are mechanistically diverse and biochemically distinct, pointing to numerous separate evolutionary origins.

  • A ‘constructive neutral evolution’ (CNE) model provides a general explanation for the emergence of diverse RNA‐editing systems.

  • A basic tenet of the CNE model is that potential RNA‐editing systems arise before there is a need for editing.

  • The emergence of an RNA‐editing system allows fixation of otherwise deleterious mutations that can be ‘repaired’ by RNA editing.

Keywords: RNA editing; evolution; coevolution; genetic drift; selection; insertional editing; substitutional editing; deamination; tRNA editing

Figure 1.

Editing of a portion of the messenger RNA encoding subunit 2 of cytochrome oxidase (COX2). (a) Insertional editing by U addition in the mitochondria of Trypanosoma brucei, a kinetoplastid protozoan. (b) Substitutional editing involving C‐to‐U changes in the mitochondria of wheat, a flowering plant. Nucleotides added (in (a)) or changed (in (b)) by editing are shown in green. Red arrows indicate differences between the nucleotide sequences of the gene and the corresponding edited RNA. Differences between the amino acid sequences inferred from the gene (‘unedited’) and from the mature mRNA (‘edited’) are shown in blue bold.



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Further Reading

Gray MW (2001) Speculations on the origin and evolution of editing. In: Bass BL (eds) RNA Editing, pp. 160–184. Oxford: Oxford University Press.

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Gray, Michael W(Jun 2013) RNA Editing: Evolutionary Implications. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0003069.pub3]