The term RNA eiting describes those molecular processes in which the information content in an RNA molecule is altered through a chemical change in the base makeup. 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 cell nucleus, cytosol, as well as in mitochondria and plastids, which are thought to have evolved from prokaryotic-like endosymbionts.