Discussion

RNA-binding proteins (RBPs) are key modulators of gene expression. Indeed, whether a particular mRNA is translated, repressed, or degraded, depends largely on its RBP interactions. This is particularly relevant for Kinetoplastids, which relies mainly on post-transcriptional mechanisms for regulation of gene expression. Here, we provide an overview of the proteins that bind to mRNAs and their putative functions in the pathogenic bloodstream form of Trypanosoma brucei. We used tethering assays to screen for proteins that play a role in post-transcriptional control. We found 90 proteins displaying a clear effect on the mRNA reporter expression, defining a catalogue of the most relevant trypanosome regulators. This list included both canonical RBPs and also proteins without RNA-related ontology. Several of the discovered repressors interacted with components of the CAF1/NOT1 deadenylation complex. To identify the repertoire of RBPs, we next obtained the mRNA-bound proteome. We identified 155 high-confidence candidates, revealing dozens of novel RBPs. Twenty-seven of these proteins were also found to modulate reporter expression in the tethering screen. Finally, we showed that 37 RBPs are evolutionary conserved from ancient trypanosome to human. Our study provides novel insights into the trypanosome mRNPs composition, architecture and function.