Translation initiation: adept at adapting

Initiation of protein synthesis requires both an mRNA and the initiator met hionyl (Met)-tRNA to be bound to the ribosome. Most mRNAs are recruited to the ribosome through recognition of the 5' m(7)G cap by a group of proteins referred to as the cap-binding complex or eIF4F. Evidence is accumulating that eIF4G, the largest subunit of the cap-binding complex, serves as a cen tral adapter by binding to various translation factors and regulators. Othe r translation factors also have modular structures that facilitate multiple protein-protein interactions, which suggests that adapter functions are co mmon among the translation initiation factors. By linking different regulat ory domains to a conserved eIF2-kinase domain, cells adapt to stress and ch anging growth conditions by altering the translational capacity through pho sphorylation of eIF2, which mediates the binding of the initiator Met-tRNA to the ribosome.