Discussion

Gene expression in trypanosomes is mainly regulated by post-transcriptional mechanisms, which makes them an excellent system for studying eukaryotic mRNA translation and degradation. RNA-binding proteins (RBPs) are known to be important in this regulation. Previously, a tethering assay was performed to identify putative trypanosome post-transcriptional regulators (1). The tethering screen yielded numerous candidate effectors, including the protein encoded by Tb927.10.14150. This protein has some similarities to yeast Bfr1p, an ER- and polysome-associated protein. Tb927.10.14150 protein is an up-regulator in the tethering screen, and showed in vivo mRNA binding (2) although it lacks canonical RNA-binding domains. We could show that the protein is essential in the bloodstream form trypanosomes, since RNAi mediated knock-down led to a growth defect. Immunofluorescence microscopy to detect a tagged version suggested that it is located in the cytoplasm, but perhaps also in the mitochondria. After pull-down and RNA sequencing, we found that most of the enriched mRNAs encode for ribosomal proteins. The regulation of mRNAs encoding for ribosomal proteins after stress is very different from that of most proteins, since they are never found in RNA-protein stress granules. We speculate that the Tb927.10.14150 protein might keep the enriched mRNAs attached to the ribosomes and thus prevent sequestration in granules.

(1) Erben et al, PLoS Pathogens 10: e1004178

(2) Lueong et al, Mol MIcrobiol 100: 457-471

(3) Fritz et al, Nucleic Acids Res 43: 8013-8032; and Minia et al (submitted).