Functions and Regulation of RNA Editing by ADAR Deaminases

One type of RNA editing converts adenosines to inosines (A -> I editing) in double-stranded RNA (dsRNA) substrates. A -> I RNA editing is mediated by adenosine deaminase acting on RNA (ADAR) enzymes. A -> I RNA editing of protein-coding sequences of a limited number of mammalian genes results in recoding and subsequent alterations of their functions. However, A -> I RNA editing most frequently targets repetitive RNA sequences located within introns and 5' and 3' untranslated regions (UTRs). Although the biological significance of noncoding RNA editing remains largely unknown, several possibilities, including its role in the control of endogenous short interfering RNAs (esiRNAs), have been proposed. Furthermore, recent studies have revealed that the biogenesis and functions of certain microRNAs (miRNAs) are regulated by the editing of their precursors. Here, I review the recent findings that indicate new functions for A -> I editing in the regulation of noncoding RNAs and for interactions between RNA editing and RNA interference mechanisms.