EIF4G-an Integrator of MRNA Metabolism?

The eukaryotic translation initiation factor, eIF4G, plays a key functional role in the initiation of cap-dependent translation by acting as an adapter to nucleate the assembly of eIF4F complex. Together with poly(A)-binding protein and eIF3, eIF4F subsequently triggers the recruitment of 43S ribosomal pre-initiation complex to the messenger RNA template. Since eukaryotes primarily regulate translation at the level of initiation, eIF4G is implicated in the control of eukaryotic gene expression. Remarkably, emerging evidence in Saccharomyces cerevisiae indicates that eIF4G also plays a key role in nuclear mRNA biogenesis and surveillance-a finding that is in agreement with its nuclear distribution. Here, we focus on the functional involvement of eIF4G in the nucleus in modulating pre-mRNA splicing, mRNA surveillance and possibly in much-debated nuclear translation. Notably, the nature of the biochemical role of this protein in the major events of cellular mRNA metabolism emphasizes that this crucial protein factor may serve as a general integrator of mRNA functional states by acting as an adapter molecule.