Abstract
Kinetoplastids rely heavily on post-transcriptional mechanisms for control of gene expression, and on RNA-binding proteins that regulate mRNA splicing, translation and decay. Trypanosoma brucei ERBP1 (Tb927.10.14150) and ERBP2 (Tb927.9.9550) were previously identified as mRNA binding proteins that lack canonical RNA-binding domains. We show here that ERBP1 is associated with the endoplasmic reticulum, like ERBP2, and that the two proteins interact in vivo. Loss of ERBP1 from bloodstream-form T. brucei initially resulted in a growth defect but proliferation was restored after more prolonged cultivation. Pull-down analysis of tagged ERBP1 suggests that it preferentially binds to ribosomal protein mRNAs. The ERBP1 sequence resembles that of Saccharomyces cerevisiae Bfr1, which also localises to the endoplasmic reticulum and binds to ribosomal protein mRNAs. However, unlike Bfr1, ERBP1 does not bind to mRNAs encoding secreted proteins, and it is also not recruited to stress granules after starvation.
Highlights
In Trypanosoma brucei, most regulation of gene expression is post-transcriptional
Our results suggest that ERBP1 and its partner ERBP2 may modulate ribosomal expression, and are both associated with the endoplasmic reticulum
ERBP1, unlike Bfr1, does not show any preference for mRNAs encoding proteins that are imported into the endoplasmic reticulum, and it does not associate with stress granules
Summary
In Trypanosoma brucei, most regulation of gene expression is post-transcriptional. Proteincoding genes are arranged in polycistronic transcription units, and mRNAs are excised by trans splicing and polyadenylation [1]. Levels of constitutively expressed proteins and mRNAs are strongly influenced by codon usage [2, 3], while regulation during development, over the cell cycle, and in response to environmental conditions is effected mainly by RNAbinding proteins. The latter often, but not always, bind sequences in 3'-untranslated regions (3'-UTRs) [1]. Bfr1p was originally recovered in a screen for high-copy-number suppression of Brefeldin A toxicity [10] It is an mRNA-binding protein that is associated with polysomes and the endoplasmic reticulum (ER) [11, 12], and is incorporated into stress granules [13]. Our results reveal that ERBP1 has both similarities with, and differences from, Bfr
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