Regulation Of Ternary Complex By Elongation Factor Ts
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Elongation factor Tu (EF-Tu), bound to GTP, delivers aminoacyl-tRNA (aa-tRNA) as a ternary complex (TC) to the translating ribosome for the purpose of decoding messenger-RNA (mRNA). As such, TC is fundamentally important to the speed and fidelity of mRNA decoding. Here, a quantitative, kinetic framework for the formation and stability of ternary complex is presented. This framework details that Elongation Factor Ts (EF Ts), a guanosine nucleotide exchange factor for EF-Tu, accelerates both the formation and dissociation of TC. This is achieved by directly loading EF-Tu?GTP to the aa-tRNA as an EF Tu/Ts?GTP?aa tRNA quaternary complex . This newly described intermediate species quickly resolves in to the canonical TC, which is then competent to participate in the decoding process. Importantly, the rate of TC formation under conditions designed to mimic cellular conditions is not rate limiting to the process of tRNA selection in the presence of EF Ts. These results suggest a new role for GEFs arguing in favor of a model wherein they catalyze the formation of activated G protien?effector complexes. Leveraging these insights, a model is proposed where EF-Ts contributes to the dissociation of the deactivated EF Tu?GDP species from the ribosome at the conclusion of the tRNA selection process.