Competition and cooperation amongst yeast elongation factors

Elongation factor 3 (EF‐3) is an essential requirement for translation in fungi. We previously reported activation of EF‐3‐ATPase by yeast ribosomes. EF‐3 interacts with both ribosomal subunits and shows high affinity for 60S subparticles. Translational inhibitors α‐sarcin, ricin and auto‐immune antibodies to GTPase‐activation center inhibit binding of EF‐2 but not of EF‐3 to yeast ribosomes. EF‐2 competes with EF‐3 for the ribosomal binding sites and inhibits EF‐3‐ATPase activity. Neomycin relieves the inhibitory effect of EF‐2 on EF‐3 function. The apparent competition between EF‐2 and EF‐3 may represent binding of these two proteins to specific conformational states of the ribosome. EF‐3 stimulates ternary complex binding to yeast ribosomes. Neither the binding of EF‐3 to ribosomes, nor the ribosome‐dependent EF‐3‐ATPase activity are influenced by EF‐1α. Three lines of experimental evidence suggest a direct interaction between EF‐1α and EF‐3. A polyclonal antibody to EF‐3 immunoprecipitates EF‐1α along with EF‐3. EF‐1α co‐migrates with GST‐EF‐3 on glutathione‐Sepharose columns. ELISA tests demonstrate an interference of EF‐3/anti‐EF‐3 interaction by EF‐1α but not by EF‐2. These results strongly suggest that the stimulatory effect of EF‐3 on the ternary complex binding to yeast ribosomes involves a direct interaction between EF‐1α and EF‐3.