A mechanism for modifying the nucleotide compositions of previously formed mRNAs by adding or deleting uridine molecules at precise sites within the coding regions of mRNAs. The phenomenon was discovered in the mitochondria of trypanosomes, and the edited molecules allowed translation of functional proteins in situations where the unedited mRNAs were defective. In trypanosomes the mtDNA is made up of 25–50 maxicircles (each 20–40 kilobases) and hundreds of minicircles (each 1–3 kilobases). The maxicircles contain the mitochondrial genes, while the minicircles encode guide RNAs, each about 40 nucleotides long. The gRNAs bind to specific sites on the mRNAs and subsequently insert or delete uridines. See Chronology, 1986, Benne et al.; 1990, Blum, Bakalara and Simpson; mitochondrial DNA, proofreading, Trypanosoma.
Subjects: Genetics and Genomics — Medicine and Health.