RNA editing.

The term RNA editing describes those molecular processes in which the information content is altered in an RNA molecule. To date such changes have been observed in tRNA. rRNA and mRNA molecules of eukaryotes, but not prokaryotes. The demonstration of RNA editing in prokaryotes may only be a matter of time, considering the range of species in which the various RNA editing processes have been found. RNA editing occurs in the nucleus, as well as in mitochondria and plastids, which are thought to have evolved from prokaryotic-like endosymbionts. Most of the RNA editing processes, however, appear to be evolutionarily recent acquisitions that arose independently. The diversity of RNA editing mechanisms includes nucleoside modifications such as C to U and A to I deaminations, as well as non-templated nucleotide additions and insertions. RNA editing in mRNAs effectively alters the amino acid sequence of the encoded protein so that it differs from that predicted by the genomic DNA sequence.