Elongation factor 2 (EF-2) has been recently shown to be extensively phosphorylated in a Ca2+ / calmodulin-dependent manner in extracts of mammalian cells (A. G. Ryazanov (1987) FEBS Lett. 214, 331-334). In the present study, we partially purified the protein kinase which phosphorylates EF-2 from rabbit reticulocytes. The molecular weight of the enzyme determined by gel filtration was about 140 000. Unlike the substrate, the EF-2 kinase had no affinity for RNA and therefore could be separated from EF-2 by chromatography on RNA-Sepharose. After chromatography on hydroxyapatite, the kinase activity became calmodulin-dependent. Two-dimensional separation of the phosphorylated EF-2 according to O'Farrell's technique revealed that there were two phosphorylation sites within the EF-2 molecule; in both cases, the phosphorylated amino acid was threonine. The EF-2 kinase differed from the four known types of Ca2+ / calmodulin-dependent protein kinases. Thus, the system of EF-2 phosphorylation represents the novel (fifth) Ca2+ / calmodulin-dependent system of protein phosphorylation. This system is supposed to be responsible for the regulation of the elongation rate of protein biosynthesis in eukaryotic cells.
All Science Journal Classification (ASJC) codes
- calmodulin-dependent protein kinase
- elongation factor 2/ Ca
- protein phosphorylation
- regulation of translation