Regulation of translation initiation in eukaryotes. One of the most important mechanisms for translational regulation in eukaryotes involves the binding of repressors to specific sites in the 3′ untranslated region (3′UTR) of the mRNA. The repressors interact with initiation factors eIF3, eIF4E, and eIF4G or with the ribosome to prevent or slow translation. The factor eIF4G mediates an interaction between eIF4E at the 5′ cap and poly(A) binding protein at the 3′ poly(A) site (see Chapter 18). This interaction is needed for efficient translation, and factors that disrupt it repress translation.