DRBD1 is the Trypanosoma brucei homologue of the Spliceosome-Associated Protein 49

The 5′-ends of all Kinetoplastid mRNAs consist of a short sequence added by trans splicing. In contrast to cis splicing in mammals, trans splicing in trypanosomes does not involve sequence-specific recognition of the branch point by the U2 snRNP. In mammalian cells and yeast, U2 snRNP is associated with the multimeric factor SF3b, which contains p14, SF3b10, SF3b14b, SAP49, SAP130, SAP145 and SAP155. The interaction between Trypanosoma cruzi p14 and SAP155 has already been characterised using the yeast 2-hybrid system. We here identify the Trypanosoma brucei RRM-protein DRBD1 as a homologue of SAP49. TAP-tagged DRBD1 co-purified with homologues of p14, SAP130, SAP145 and SAP155. Tagged DRBD1 was found in the nucleus; RNAi targeting DRBD1 inhibited trypanosome growth and caused a very mild splicing defect.