Analysis of eIF4E-family members in fungi contributes to their classification in eukaryotes

The kingdom of fungi contains highly diverse species. However, fundamental processes sustaining life such as RNA metabolism are much less comparatively studied in Fungi than in other kingdoms. A key factor in the regulation of mRNA expression is the cap-binding protein eIF4E, which plays roles in mRNA nuclear export, storage, and translation. The advent of massive genomics has unveiled a constellation of eIF4E-family members across eukaryotes. However, how this protein diverged into fungal species remains largely unexplored. Here, we studied the genome of 538 species from six evolutionarily distant phyla and retrieved 1462 eIF4E cognates. The analyzed species contained 1 to 7 paralogs. We sorted all cognates in six phylogenetically coherent clades, that we termed Class I to VII (mammalian Class III was absent in Fungi). Proteins from Classes IV to VII did not match the current eIF4Es classification that is based on variations in the residues equivalent to W43 and W56 of the human protein. eIF4Es from other eukaryotes do not fit into this classification either. Thus, we have updated the eIF4E categorization based on cladistics and the presence of cap-binding amino acids to better fit eIF4E's diversity across eukaryotes. Finally, we predicted the structure of the global protein and the cap-binding pocket and experimentally tested the ability to rescue the lack of endogenous eIF4E in Saccharomyces cerevisiae of representative members of each of the six classes of fungal eIF4E.