Protein synthesis in yeast. I. Purification and properties of elongation factor 3 from Saccharomyces cerevisiae.

Elongation factor 3 from the yeast Saccharomyces cerevisiae was purified over 230-fold from a high speed supernatant fraction. The homogeneity of the protein was shown by gel filtration and sedimentation equilibrium analysis of the native protein and by sodium dodecyl sulfate gel electrophoresis of the denatured protein. The molecular weight of the protein was estimated to be 125,000 by the above-mentioned methods. The protein consists of a single polypeptide chain. Amino acid analysis revealed no unusual features. Antibody raised against the purified factor showed a single cross-reacting band with the characteristic hexagonal pattern in an Ouchterlony double diffusion plate. The immune serum had no reactivity against the other two elongation factors (EF). The polymerization reaction was inhibited by the anti-EF3. Addition of excess EF3 could overcome this effect. Factor 3 is absolutely required by the yeast ribosomes for polyphenylalanine synthesis. Ribosomes from other eukaryotes do not require this protein. The function of the third factor in polyphenylalanine synthesis cannot be defined at this time. The protein showed ribosome-dependent GTPase and ATPase activities. Studies of partial reactions showed that EF3 was not required for Phe-tRNA binding to ribosomes, peptide bond formation, or translocation. Nucleotide exchange by EF1 was not stimulated by EF3.