Specific cleavage of pre-edited mRNAs in trypanosome mitochondrial extracts.

RNA editing in Trypanosoma brucei is a posttranscriptional processing event that results in the addition and deletion of uridine residues within several mitochondrial mRNAs. We have examined reactions involving pre-edited precursor RNAs in vitro. In this study, we report specific cleavage of pre-edited cytochrome b (CYb), cytochrome oxidase subunit II (COII), and cytochrome oxidase subunit III (COIII) mRNAs when incubated with T. brucei mitochondrial extracts. The pre-edited CYb RNA was cleaved near the 3'-most uridine addition sites, within the region where editing would be expected to commence. Pre-edited COII mRNA was similarly cleaved adjacent to its small editing domain, while pre-edited COIII RNA was cleaved at multiple sites in the region where uridine addition and deletion occurs in vivo. In contrast, edited versions of CYb, COII, and COIII RNAs were not cleaved within the editing domains. Such differential cleavage of the edited and pre-edited forms of these mRNAs suggests either a direct involvement in RNA editing or involvement in another aspect of mitochondrial gene expression requiring cleavage of pre-edited RNAs.