Stimulation of yeast EF-3 factor by mammalian ribosomes

The ATPase activity of yeast elongation factor 3 (EF-3) which is a specific component of fungal translational machinery and normally requires homological ribosomes, can be stimulated by mammalian ribosomes (from the rabbit liver). The level of such heterological stimulation is strongly dependent on ATP concentration and the ratio of ribosomes to EF-3 and achieves 50% of homological one under optimum conditions. ATP concentration dependence, modes of inhibition by ADP and pH-dependence have been found to differ for EF-3 activity stimulated by ribosomes and rabbit ribosome-associated ATPase. It may reflect the necessity of [EF-3*ATP*Rs]-complex formation while in the case of ribosomal ATPase both catalytic center and the enhancement element are located in the ribosome. Both 40S and 60S subunits take part in stimulation, contrary to the homological system, where only 40S subunits play crucial role in this process. The data presented indicate that the binding site and enhancement element(s) for EF-3 in the ribosomes are concerved in evolution, though with a significant change in the binding affinity.