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.
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