Identification of an actin-binding protein from Dictyostelium as elongation factor 1a.

INDIRECT evidence has implicated an interaction between the cytoskeleton and the protein synthetic machinery1–8. Two recent reports have linked the elongation factor la (EF-la) which is involved in protein synthesis, with the microtubular cytoskeleton7–8.In situ hybridization has, however, revealed that the messages for certain cytoskeletal proteins are preferentially associated with actin filaments6. ABP-50 is an abundant actin filament bundling protein of native relative molecular mass 50,000 (50K)9 isolated from Dictyostelium discoideum. Immunofluorescence studies show that ABP-50 is present in filopodia and other cortical regions that contain actin filament bundles9,10. In addition, ABP-50 binds to monomeric actin in the cytosol of unstimulated cells and the association of ABP-50 with the actin cytoskeleton is regulated during chemotaxis10. Through complementary DNA sequencing and subsequent functional analysis, we have identified ABP-50 as D. discoideum EF-la. The ability of EF-la to bind reversibly to the actin cytoskeleton upon stimulation could provide a mechanism for spatially and temporally regulated protein synthesis in eukaryotic cells.