CTS tag-based methods for investigating mitochondrial RNA modification factors in Trypanosoma brucei

Unicellular parasite Trypanosoma brucei maintains an elaborate mitochondrial mRNA processing pathway including 3'-5' exonucleolytic trimming of primary precursors, 5' and 3' modifications, and, in most cases, massive U-insertion/deletion editing. Whereas the role of editing in restoring protein coding sequence is apparent, recent developments suggest that terminal modifications are equally critical for generating a stable translationally competent messenger. The enzymatic activities responsible for 5' pyrophosphate hydrolysis, 3' adenylation and uridylation, and 3'-5' decay are positively and negatively regulated by pentatricopeptide repeat-containing (PPR) proteins. These sequence-specific RNA binding factors typically contain arrays of 35-amino acid repeats each of which recognizes a single nucleotide. Here, we introduce a combinatorial CTS affinity tag, which underlies a suite of methods for PPR proteins purification, in vivo RNA binding sites mapping and sub-cellular localization studies. These approaches should be applicable to most trypanosomal RNA binding proteins.