eEF1AeEF2

eEF1AeEF2 refers to the two eukaryotic elongation factors eEF1A and eEF2, which perform essential yet distinct steps in the translation elongation cycle. In eukaryotes, these factors are encoded by separate genes (for example EEF1A1 and EEF1A2 for eEF1A, and EEF2 for eEF2) and are highly conserved across eukaryotic species. They coordinate with other components of the ribosome to ensure accurate and efficient protein synthesis, while also participating in additional cellular processes beyond translation.

eEF1A is responsible for delivering aminoacyl-tRNA to the ribosome. In its active form, eEF1A binds GTP and aminoacyl-tRNA to form a ternary complex that associates with the ribosome's A site. Upon codon recognition, GTP is hydrolyzed, triggering conformational changes that enable tRNA accommodation and subsequent peptide bond formation. The GDP-bound eEF1A is recycled back to the GTP-bound state by the guanine nucleotide exchange factor complex eEF1B. eEF1A exists as multiple isoforms (notably eEF1A1 and eEF1A2 in humans) and also has noncanonical roles, including interactions with the actin cytoskeleton and involvement in viral replication. Post-translational modifications modulate its activity and interactions.

eEF2 drives the translocation step of elongation. As a GTPase, eEF2 promotes the movement of the ribosome along the mRNA after peptide bond formation, shifting the peptidyl-tRNA from the A site to the P site. This activity is tightly regulated; eEF2 can be inactivated by phosphorylation via eEF2 kinase under stress conditions. Eukaryotic eEF2 is a target of certain ribosome-inactivating toxins, such as diphtheria toxin and Pseudomonas exotoxin A, which modify a conserved diphthamide residue on eEF2 and block translocation.

Together, eEF1AeEF2 coordinate the core elongation steps while linking translation to broader cellular regulation and responses.