The endoplasmic reticulum-associated mRNA-binding proteins ERBP1 and ERBP2 interact in bloodstream-form Trypanosoma brucei

Kinetoplastids rely heavily on post-transcriptional mechanisms for control of gene expression, and on RNA-binding proteinsthat regulate mRNA splicing, translation and decay. Trypanosoma bruceiERBP1 (Tb927.10.14150) and ERBP2 (Tb927.9.9550) were previously identified as mRNA binding proteins that lack canonical RNA-binding domains. We here show 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. Results from a pull-down of tagged ERBP1 suggest that it preferentially binds to ribosomal proteinmRNAs. The ERBP1 sequence resembles that of Saccharomyces cerevisiae Bfr1, which also localises to the endoplasmic reticulumand binds to ribosomal proteinmRNAs. However, unlike Bfr1, ERBP1 does not bind to mRNAs encoding secreted proteins, and it is also not recruited to stress granulesafter starvation.