Hydrolysis of GTP on elongation factor Tu*ribosome complexes

In the presence of Escherichia coli ribosomes and elongation factor (EF) Tu, 2'(3'O-L-phenylalanyladenosine (AdoPhe), the 3'-terminal portion of Phe-tRNAPhe, promotes the hydrolysis of GTP. The reaction requires the presence of both 30S and 50S ribosomal subunits and of proteins L7/L12 on the 50S subunit, is unaffected by mRNA (poly(uridylic acid)), and is strongly stimulated by EF-Ts. It is proposed that the AdoPhe-dependent GTP hydrolysis, like that promoted by aminoacyl-tRNA, is mediated by a ternary complex with EF-Tu and GTP; however, in contrast to aminoacyl-tRNA, AdoPhe is probably not retained by ribosomes after GTP hydrolysis. Phe-tRNAPhe or N-acetyl-Phe-tRNAPhe bound to the ribosomal acceptor site do not inhibit, but even stimulate, GTP hydrolysis by AdoPhe-EF-Tu*GTP. Thus, the binding site for EF-Tu on the ribosome is probably available for interaction with AdoPhe EF-Tu GTP regardless of whether the nearby acceptor site is vacant or occupied with aminoacyl-tRNA or peptidyl-tRNA. The results demonstrate the critical role of the 3'-terminal region of aminoacyl-tRNA in activating the EF-Tu- plus ribosome-de- pendent GTPase. Elongation factor (EF) Tu, a supernatant protein from Esche- richia coli, promotes the mRNA-directed binding of amino- acyl-tRNA to the ribosomes (see ref. 1 for a review). The binding is mediated by a ternary aminoacyl-tRNA-EF-Tu-GTP complex and is followed by the hydrolysis of the complexed