Comparative analysis of ATPase of yeast elongation factor 3 and ATPase associated with Tetrahymena ribosomes.

Elongation factor 3 (EF-3) is a unique and essential requirement of the fungal translational apparatus. The biochemical function of EF-3 has recently been defined. The protein removes deacylated tRNA from the ribosomal exit site (E-site) thus facilitating occupation of the ribosomal A-site by aa-tRNA. A functional homolog of yeast EF-3 has not been identified in non-fungal species. Yeast EF-3 is a ribosome-dependent ATPase that can also accept GTP and ITP as substrates. The function of EF-3 in ribosomal reactions requires ATP hydrolysis. An ATPase activity associated with higher eukaryotic ribosomes has been claimed to be a direct functional homolog of yeast EF-3. Comparative analysis of biochemical, immunological and functional properties of ATPase activity associated with the ribosomes isolated from the ciliated protozoan Tetrahymena pyriformis with that of yeast EF-3 ATPase indicates that these two activities are significantly different. Results reported in this communication strongly suggest that the ribosome associated ATP hydrolytic activity of Tetrahymena pyriformis is not a functional homolog of yeast EF-3.