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Abstract:
Most eukaryotic mRNAs are translated by a cap-dependent mechanism, which requires recognition of the 5′ cap structure of the mRNA by eIF4E. Due to its crucial role in translation, eIF4E is a major target of regulation. One of the most prominent mechanisms regulating eIF4E activity is through its interaction with numerous proteins termed eIF4E-interacting proteins (4E-IPs). By competing with eIF4G for eIF4E binding, 4E-IPs act in general as translational repressors, although additional functions have been described. In this chapter, we discuss recent functional, phylogenetic and structural evidence that throws light on the evolution of 4E-IPs and evolutionary recurring themes. Phylogenetic analysis suggests that the first identified 4E-IPs, the mammalian 4E-binding proteins (4E-BPs), appeared as a single-copy gene in the last common ancestor of Amoebozoa, Glaucocystophyta, Fungi and Metazoa. 4E-BP is found in all Metazoans except Nematoda. It is found in glaucocystophytes, but has been lost in Viridiplantae. It is lost in most fungi, although it can be found in basidiomycetes as well as some glomeromycetes and zygomycetes. 4E-BP has been duplicated in vertebrates with up to six cognates found. 4E-BP seems to be absent, not lost, in most protist lineages since it has not been found in lineages thought to be at the root of the eukaryotes. Additional 4E-IPs, unrelated to 4E-BP, evolved independently in a lineage-specific manner, perhaps by a process of molecular tinkering, i.e., by gene duplication of preexisting proteins from different cellular processes and later in evolution incorporated into translation. Multiple duplications of eIF4E during eukaryotic radiation might have contributed, to some extent, to 4E-IP’s evolution. Some 4E-IPs are shared by different taxa, such as the eIF4E transporter, neuroguidin and Maskin, which are present in Amoebozoa, some/all fungi and the metazoan lineages. Unique lineage-specific 4E-IPs have evolved independently in some taxonomic groups such as Eap1p and p20 in yeasts, SPN-2 in C. elegans and Bicoid in higher Dipterans. Neuroguidin is the only 4E-IP represented in all eukaryotic lineages. Despite the diversity in function, sequence and origin, recent studies have revealed that 4E-IPs exhibit common binding principles when complexed with eIF4E.
