A-to-I editing of coding and non-coding RNAs by ADARs

ADAR enzymes convert adenosine to inosine (A-to-I editing) at numerous double-stranded Alu repeats in human transcripts, thereby affecting many cellular processes. Primary microRNAs (miRNAs) are also edited, and ADAR1 directly interacts with Dicer, resulting in the modulation of miRNA expression and activity and of downstream gene expression programmes during embryogenesis. Adenosine deaminases acting on RNA (ADARs) convert adenosine to inosine in double-stranded RNA. This A-to-I editing occurs not only in protein-coding regions of mRNAs, but also frequently in non-coding regions that contain inverted Alu repeats. Editing of coding sequences can result in the expression of functionally altered proteins that are not encoded in the genome, whereas the significance of Alu editing remains largely unknown. Certain microRNA (miRNA) precursors are also edited, leading to reduced expression or altered function of mature miRNAs. Conversely, recent studies indicate that ADAR1 forms a complex with Dicer to promote miRNA processing, revealing a new function of ADAR1 in the regulation of RNA interference.