RNAEditing

RNA editing refers to post-transcriptional modifications that change the nucleotide sequence of an RNA molecule relative to its DNA template. These changes are not due to DNA mutations and are distinct from standard RNA processing steps such as splicing or polyadenylation. The most common forms in animals are base substitutions, notably adenosine-to-inosine (A-to-I) editing and cytidine-to-uridine (C-to-U) editing.

A-to-I editing is carried out by adenosine deaminases acting on RNA (ADARs), primarily ADAR1 and ADAR2. They modify adenosines within double-stranded RNA regions, with inosine interpreted as guanosine by cellular machinery. This can alter coding potential, splicing, RNA stability, or localization. Some well-characterized recoding events occur in the brain, such as changes in ion channel and receptor transcripts that can affect neural function.

C-to-U editing is mediated by cytidine deaminases, including the APOBEC family. In mammals, APOBEC1 edits certain mRNAs such as apolipoprotein B (ApoB), producing two protein isoforms via site-specific editing. In plants and algae, extensive C-to-U editing occurs in mitochondrial and chloroplast transcripts and is guided by specific RNA-editing factors, playing a critical role in organellar gene expression.

Other RNA modifications, such as pseudouridylation and various methylations, are related forms of RNA editing in a broader sense but involve chemical alterations rather than simple base substitutions. RNA editing is detected by high-throughput sequencing and chemical mapping methods and is studied for its roles in development, physiology, and disease. Aberrant editing has been linked to neurological disorders and cancer, highlighting its regulatory significance and therapeutic interest.