KREPA6 functions in RNA editing catalytic complex structural organization and gRNA utilization in <i>Trypanosoma brucei</i>

Functional mitochondrial mRNAs in Trypanosoma brucei are generated by the post-transcriptional guide RNA (gRNA) directed insertion and deletion of uridine residues, called RNA editing, that is catalyzed by three closely related multiprotein RNA Editing Catalytic Complexes (RECCs). These RECCs contain a common set of 12 proteins including KREPA6 which is largely comprised of an oligonucleotide binding (OB)-fold domain with a predicted intrinsically disordered region (IDR) at its C-terminus. Here we show that certain single amino acid substitutions throughout KREPA6 or deletion of the IDR inhibit the growth and viability of bloodstream form (BF) parasites. These mutations variously impact RECC structure, many alter but do not eliminate RNA editing, and some result in differential utilization of gRNAs. The results indicate that KREPA6 protein has multiple functions some of which stem from its interactions with multiple RECC proteins and perhaps with substrate RNA in each of the three different RECCs. These functions likely involve dynamic interactions of KREPA6 with key domains of other RECC proteins, other editing proteins, and with messenger RNA/gRNA substrates during the multiple catalytic and noncatalytic steps that occur during the complicated editing process.