Abstract
Incubation of a ribosome‐free extract of rabbit reticulocytes or rat liver with [γ‐32P]ATP and Ca2+ results in incorporation of 32P predominantly into a single polypeptide of Mr ∼ 100 000. This polypeptide is identified as elongation factor 2 (EF‐2). Phosphorylation of EF‐2 is strictly Ca2+‐dependent and can be inhibited by the calmodulin antagonist trifluoperazine. It is suggested that the Ca2+/calmodulin‐dependent phosphorylation of EF‐2 is involved in regulation of protein biosynthesis.