One of the significant amendments to the central dogma of the molecular biology was the discovery of the RNA editing process in different genetic systems. Whereas other forms of co- and posttranscriptional modifications of messenger RNA (mRNA) (capping, polyadenilation, splicing) retain the correspondence of the primary structure of exon and final transcript, RNA editing disturbs this correspondence changing the primary structure of mRNA after its transcription. The variants of RNA-editing mechanisms are various and include site-specific insertions and deletions of one or several nucleotides (insertion-deletion editing) as well as specific modifications of nucleosides such as C-->U and A-->I deamination or U-->C transamination (conversion editing). These mechanisms differ greatly in different genetic systems but they always result in synthesis of functionally valuable proteins from "incorrect" genes and, correspondingly, can play a significant role in regulation of their expression.