The present review surveys the available data on the involvement of adenine 
deamination in RNA molecules in the formation of structurally and functionally 
diverse RNA and protein subforms in eukaryotic cells. Deamination of adenine by 
adenosine deaminases that act on RNA (ADARs) leads to the conversion of adenine 
into inosine (A-I editing) recognized by the splicing and translation systems as 
guanine. This may modify splicing sites in pre-mRNA and codons in translated 
regions ofmRNA and also affect the RNA secondary structure. Apart from mRNA, 
editing also involves microRNAs whose regulatory functions in multicellular 
animals are associated with the inhibition of transcription of target genes or 
with the degradation of certain RNA transcripts. ADARs can inhibit the 
production of mature microRNAs or modify microRNAs so that their specificity to 
target genes is altered. Adenosine deaminases editing adenines in transport RNAs 
(ADATs) convert adenine into inosine in tRNAs of all eukaryotes; as a result, 
the diversity of tRNA forms in the cell increases.