RNA EDITING IN KINETOPLASTID PROTOZOA

Mitochondrial transcripts in kinetoplastids undergo remarkable posttra nscriptional editing by uridylate insertion and deletion. The often dr amatic remodelling of pre-mRNA sequences is directed by small guide RN As (gRNAs) to produce mature mRNAs. In vitro analyses of editing have been used to determine the mechanism of editing and show that editing occurs by a series of enzyme-catalyzed steps. They also show that chim eric gRNA/mRNA molecules are not editing intermediates as proposed but are aberrant end products of editing. The complexes and molecules tha t catalyze editing are now being identified and characterized. The ori gin of editing, its developmental regulation which helps control the s witching between terminal respiratory systems during the life cycle of trypanosomes, and other areas for future study are discussed.