RNA Editing in African Trypanosomes: A U-ser’s G-U-ide

Abstract

Of the chemical repertoire of RNA processing pathways, one reaction cycle stands out due to its idiosyncratic features. The process has evolved within the mitochondria of only one clad of organisms, the kinetoplastid protozoa (Excavata, Euglenozoa), which include the African trypanosome, the causative agent of sleeping sickness. The process can be categorized as an RNA editing-type reaction. It is characterized by the insertion and/or deletion of uridine nucleotides into otherwise nontranslatable mRNAs. Kinetoplastid RNA editing relies on an exclusive class of trans-acting, small noncoding RNA molecules known as guide RNAs. Furthermore, a unique molecular machinery, the editosome, catalyzes the process. Editosomes represent high-molecular-mass multienzyme assemblies that provide a catalytic surface for the individual steps of the editing reaction cycle. Here I review the current mechanistic model of the editing reaction and I summarize the molecular components and accessory factors of the editosome machinery. Special emphasis is put on the recent discovery of the molecular structure of the editing complex, which allows a first correlation of structural features with functional characteristics.