RNA EDITING IN TRYPANOSOMES

The nucleotide sequence of mitochondrial pre-mRNAs in trypanosomes is posttranscriptionally edited by the insertion and deletion of uridylat e (U) residues. In some RNAs editing is limited to small sections but in African trypanosomes, such as Trypanosoma brucei, 9 of the 18 known mitochondrial mRNAs are created by massive editing which can produce more than 50% of the coding sequence. In all cases, however, RNA editi ng is a key event in gene expression during which translatable RNAs ar e generated. The information for the editing process and possibly also the inserted Us are provided by small guide RNAs, which are encoded i n both the maxicircle and minicircle components of the trypanosome mit ochondrial DNA. Current models of editing are largely based on the cha racteristics of partially edited RNAs and on the occurrence in vivo an d the possibility of synthesis in vitro of chimeric molecules in which a guide RNA is covalently linked through its 3' oligo(U) tail to an e diting site in pre-mRNA. In this paper, I will review the research in this rapidly growing field and illustrate how different interpretation s of the available data can lead to different views of the mechanism a nd the biochemistry of the editing process.