Characterization of elongation factor 1 from yeast

Two species of elongation factor 1 (EF-1) differing in molecular weight have been obtained from the postribosomal supernatant fraction of yeast by chromatography on Sephadex G-200. These two forms are present in approximately equal amounts and both appear to be of cytoplasmic origin. Preparations of the higher and lower molecular weight forms of EF-1 catalyze the poly(U)-directed binding of N-acetylphenylalanylt-RNA (AcPhe-tRNA) to yeast ribosomes. The AcPhe-tRNA binding activity of these preparations is consistently lower than the phenylalanyl-tRNA (Phe-tRNA) binding activity and is more sensitive to N-ethylmaleimide. However, the AcPhe-tRNA binding activity co-purifies with EF-1 on phosphocellulose and has the same heat inactivation profile. Several lines of evidence indicate that the AcPhe-tRNA is bound to the acceptor site of the ribosomes. These and other data strongly suggest that yeast EF-1 is capable of catalyzing the binding of both Phe-tRNA and AcPhe-tRNA to ribosomes.