Discussion

It is well known that the control of gene expression in Trypanosomatids is primarily mediated by post-transcriptional processes that regulate, among other events, the recruitment of mRNAs for translation. In other eukaryotes, mRNA recruitment is mediated by the mRNA cap binding protein, eIF4E, part of the eIF4F complex. In trypanosomatids, six eIF4E homologues were identified, with two of those (EIF4E3 and EIF4E4) implicated during translation initiation. Their potential to selective recruit distinct mRNA populations for translation, however, remain undefined. The aim of this study then was to investigate which mRNA populations bind to EIF4E3 and EIF4E4 in Trypanosoma brucei. Independent experiments were carried out using the native or ectopically expressed tagged proteins in immunoprecipitation assays which were followed by RNA extraction and SOLiD or Illumina next generation sequencing, respectively. The Gene Ontology molecular function annotation was then used to identify the different mRNA populations. The results indicate that although there are mRNAs co-precipitating with both proteins, EIF4E4 seems to associate preferentially with mRNAs encoding abundant housekeeping proteins with structural roles, such as the ribosomal proteins. In contrast, mRNAs bound to EIF4E3 are enriched in those coding for proteins with catalytic and binding activities. A complementary profile can then be observed, consistent with different populations of mRNAs bound to each protein.