Direct Evidence of an Elongation Factor-Tu/Ts-GTP-Aminoacyl-tRNA Quaternary Complex [Molecular Biophysics]

July 2nd, 2014 by Burnett, B. J., Altman, R. B., Ferguson, A., Wasserman, M. R., Zhou, Z., Blanchard, S. C.

During protein synthesis, elongation factor-Tu (EF-Tu) bound to GTP chaperones the entry of aminoacyl-tRNA (aa-tRNA) into actively translating ribosomes. In so doing, EF-Tu increases the rate and fidelity of the translation mechanism. Recent evidence suggests that EF-Ts, the guanosine nucleotide exchange factor (GEF) for EF-Tu, directly accelerates both the formation and dissociation of the EF-Tu-GTP-Phe-tRNAPhe ternary complex (1). A central feature of this model is the existence of a quaternary complex of EF-Tu/Ts-GTP-aa-tRNAaa. Here, through comparative investigations of phenylalanyl-, methionyl- and arginyl-ternary complexes, and the development of a strategy to monitor their formation and decay using fluorescence resonance energy transfer, we reveal the generality of this newly described EF-Ts function and the first direct evidence of the transient quaternary complex species. These findings suggest that EF-Ts may regulate ternary complex abundance in the cell through mechanisms that are distinct from its GEF functions.