5.1. Structure and Functioning of eIF4G. The process of translation can be divided in different steps: initiation, elongation, termination and ribosome recycling. The synthesis of cellular proteins is highly regulated, and in this sense, the most precisely controlled step is the initiation of translation (for a recent review, see [81, 82] ). For most eukaryotic mRNAs, the initiation of translation commences with the recognition of the cap structure ( 7 mGpppN) and the poly(A) tail by the heterotrimeric complex eIF4F and the poly(A)-binding protein (PABP), respectively, followed by the recruitment of the 43S preinitiation complex containing the 40S ribosomal subunit, the ternary complex Met-tRNA Met i -eIF2-GTP, and the eukaryotic initiation factors (eIFs), 1, 1A, 3, and 5. Then, the preinitiation complex scans along the 5 untranslated region until an AUG initiation codon is encountered in a favourable context. The perfect complementarity between the AUG start codon and the anticodon of Met-tRNA i leads to the arrest of scanning and the hydrolysis of GTP in the ternary complex. The release of eIF2-GDP and other factors triggers the interaction of the preinitiation complex with the 60S ribosomal subunit to form the 80S initiation complex, proceeding to translation of the mRNA coding region.