Elongation factor 1 beta is an actin-binding protein

A 17 kDa polypeptide found in association with actin in cellular extracts o f Dietyostelium discoideum was identified as a proteolytic fragment of eEF1 beta. Antibody elicited against the 17 kDa protein reacted with a single 2 9 kDa polypeptide in Dictyostelium, indicating that the 17 kDa peptide aris es from degradation of a larger precursor. The cDNA isolated from a Dictyos telium library using this antibody as a probe encodes Dictyostelium elongat ion factor lp. Amino acid degradation of the 17 kDa protein fragment confir med the identity of the protein as eEF1 beta. Direct interaction of cEF1 be ta with actin in vitro was further demonstrated in mixtures of actin with t he 17 kDa protein fragment of Dietyostelium eEF1 beta, recombinant preparat ions of Dietyostelium eEF1 beta expressed in Escherichia coli, and the inta ct eEF1 beta gamma complex purified from wheat germ. Localization of cEF1 b eta in Dictyostelium by immunofluorescence microscopy reveals both diffuse cytoplasmic staining, and some concentration in the cortical and hyaline cy toplasm. The results support the existence of physical and functional inter actions of the translation apparatus with the cytoskeleton, and suggest tha t eEF1 beta may function in a dual role both to promote the elongation phas e of protein synthesis, and to interact with cytoplasmic actin. (C) 2001 El sevier Science B.V. All rights reserved.