The 100-kDa protein, whose phosphorylation precedes the fusion of chick embryonic myoblasts, is the eukaryotic elongation factor-2.

We have previously shown that Ca2+/calmodulin-dependent phosphorylation of the 100-kDa protein dramatically increases during the early period of myoblast fusion and inhibition of the protein phosphorylation prevents the fusion. Here, we show that the protein phosphorylation occurs exclusively at Thr residue(s) and the purified 100-kDa protein can be ADP-ribosylated upon treatment with diphtheria toxin. Furthermore, the 13 N-terminal amino acid sequence of the 100-kDa protein, N-Val-Asn-Phe-Val-Asp-Gln-Ile-Arg-Ala-Ile-Met-Asp-Lys, exactly matches with that of elongation factor-2 from rat and hamster. These results indicate that the 100-kDa protein in chick embryonic myoblasts is identical to the eukaryotic elongation factor-2.