Mechanism of elongation factor 2 (EF‐2) inactivation upon phosphorylation Phosphorylated EF‐2 is unable to catalyze translocation

Abstract
Previously we have found that elongation factor 2 (EF‐2) from mammalian cells can be phosphorylated by a special Ca2+/calmodulin‐dependent protein kinase (EF‐2 kinase). Phosphorylation results in complete inactivation of EF‐2 in the poly(U)‐directed cell‐free translation system. However, the partial function of EF‐2 affected by phosphorylation remained unknown. Here we show that phosphorylated EF‐2, unlike non‐phosphorylated EF‐2, is unable to switch ribosomes carrying poly(U) and Phe‐tRNA in the A site to a puromycin‐reactive state. Thus, phosphorylation of EF‐2 seems to block its ability to promote a shift of the aminoacyl(peptidyl)‐tRNA from the A site to the P site i.e. translocation itself.