RNA-editing-associated protein 1 null mutant reveals link to mitochondrial RNA stability.

In trypanosomatids, uridylate residues are post-transcriptionally added to or deleted from pre-mRNAs during the complex process of RNA editing. Editing is carried out exclusively in the mitochondrion of these parasites and involves numerous proteins assembled into protein and ribonucleoprotein complexes. Previously we identified RNA-editing-associated protein -1 (REAP-1), an RNA binding protein found in the mitochondrion of Trypanosoma brucei. REAP-1 was shown to specifically recognize and bind to pre-mRNAs that require editing and was proposed to act as a recruitment factor to deliver pre-mRNAs to editing complexes. To help define the role of REAP-1, we have now constructed REAP-1 null mutants. We show that the null mutants, although viable, have a significant growth defect. RNA levels within the mitochondrion were evaluated using reverse transcriptase real-time PCR. Surprisingly, the results show that mitochondrial RNA levels are increased, regardless of the editing status of the RNA. All RNA tested, whether unedited, edited, or never edited were increased in the mutant cell line relative to wild-type levels. This study provides the first evidence for a role of REAP-1 in RNA metabolism.