Phosphorylation of elongation factor 2: a key mechanism regulating gene expression in vertebrates.

Elongation factor 2 (eEF-2) is a 100-kD protein that catalyzes the ribosomal translocation reaction, resulting in the movement of ribosomes along mRNA. eEF-2 is the target for a very specific Ca2+/calmodulin-dependent eEF-2 kinase. Phosphorylation of eEF-2 makes it inactive in translation, which suggests that protein synthesis can be regulated by Ca2+ through eEF-2 phosphorylation. Recent data demonstrate that eEF-2 phosphorylation can be involved in cell-cycle regulation and other processes where changes of intracellular Ca2+ concentration induce a new physiological state of a cell. The main role of eEF-2 phosphorylation in these processes is temporary inhibition of overall translation in response to transient elevation of the Ca2+ concentrations in the cytoplasm. Temporary inhibition of translation may trigger the transition of a cell from one physiologic state into another because of the disappearance of short-lived repressors and thus the activation of expression of new genes.