Insights from a Paradigm Shift: How the Poly(A)-Binding Protein Brings Translating mRNAs Full Circle

Figure 2

Detailed depiction of the steps during translation initiation. In the first step, eIF4E, eIF4G, eIF4A, and eIF4B are recruited to the 5′-cap of an mRNA. Using the hydrolysis of ATP, eIF4A assisted by eIF4B removes secondary structure in the 5′-UTR. The interactions between PABP and eIF4G as well as eIF4B that circularize the mRNAs are depicted. The 43 S complex, containing the 40 S subunit, eIF1, eIF1A, eIF2, eIF3, and eIF5, is recruited to the 5′-cap through the interaction between eIF3 and eIF4G and the 40 S subunit scans down the 5′-UTR. Whether eIF4F remains bound at the 5′-cap is not known. Upon location of the first AUG in a good context, the initiation factors are released and eIF5B assists the joining of the 60 S subunit to form the 80 S ribosome at which point protein synthesis begins. A key to the initiation factors depicted is included in the figure.