RNA editing-associated protein 1 is an RNA binding protein with specificity for preedited mRNA

RNA editing in the mitochondria of kinetoplastids involves the addition and deletion of uridines at specific sites as directed by guide RNAs (SRNAs). Ample evidence shows that ribonucleoprotein (RNP) complexes carry out this posttranscriptional processing. One component of RNA editing complexes is R EAP-1, a protein of previously unknown function found primarily in mRNA con taining editing complexes. We now show that REAP-1 is an RNA binding protei n and map the binding activity to the amino-terminal third of the protein. REAP-1 binds to poly(G) and single-stranded guanosine rich RNAs. Data prese nted here demonstrates that preedited RNAs are the preferred substrate for REAP-1. The results suggest a model in which the role of REAP-1 is to bring preedited mRNAs into the editing complex.