Recent observations indicate that the stoichiometry for the complex between EF-Tu · GTP and aminoacyl-tRNA (aa-tRNA) changes with temperature. At 37°C two EF-Tu · GTPs bind one aa-tRNA in an extended ternary complex, but at 0°C the complex has 1:1 stoichiometry. However, the present experiments show that there are two GTPs hydrolyzed on EF-Tu per peptide bond in poly(Phe) synthesis at 37°C as well as at 0°C. This indicates two different pathways for the enzymatic binding of aa-tRNA to the A-site on the ribosome.
