A unique mRNA decapping complex in trypanosomes

Removal of mRNA 5’ caps primes transcripts for degradation and is central for regulating gene expression in eukaryotes. The canonical decapping enzyme DCP2 is stringently controlled by assembly into a dynamic multi-protein complex together with the 5´-3´exoribonuclease Xrn1. Kinetoplastida lack DCP2 orthologues but instead rely on the ApaH-like phosphatase ALPH1 for decapping. The enzyme is composed of a catalytic domain flanked by C-terminal and N-terminal extensions. Here we analyse the ALPH1 interactome by BioID proximity labelling for the full length protein and truncated versions in order to assign domain specific interactions. We show that Trypanosoma brucei ALPH1 acts in a complex composed of the trypanosome XRN1 ortholog XRNA and four proteins that are unique to Kinetoplastida.The interactome is validated by reverse experiments targeting T. brucei and T. cruzi XRNA by affinity capture and, additionally, the ALPH1 interacting CMGC-family kinase by BioID.