Aminoacyl-tRNAs Are Escorted to the Ribosome by Elongation Factor EF-Tu

During protein synthesis in prokaryotes, the delivery of aminoacyl-tRNAs (aa-tRNAs) to the ribosome is a critical step in translation elongation. This process is facilitated by specialized elongation factors that ensure accurate and efficient decoding of mRNA codons.

Role of EF-Tu in Translation

• EF-Tu (Elongation Factor Thermo Unstable) is the primary elongation factor responsible for escorting aa-tRNAs to the ribosome’s A site.

• EF-Tu forms a ternary complex with GTP and an aa-tRNA, protecting the aminoacyl end of the tRNA and delivering it to the ribosome.

• Upon correct codon-anticodon pairing, EF-Tu hydrolyzes GTP to GDP, undergoes a conformational change, and releases the aa-tRNA for peptide bond formation.

• EF-Tu then recycles by exchanging GDP for GTP, a process catalyzed by EF-Ts.

Why Other Elongation Factors Are Not Responsible for aa-tRNA Delivery

• EF-Ts: Acts as a guanine nucleotide exchange factor (GEF) that regenerates EF-Tu by exchanging GDP for GTP; it does not escort aa-tRNAs.

• EF-G: Facilitates translocation of the ribosome along mRNA after peptide bond formation, not aa-tRNA delivery.

• eEF-2: The eukaryotic homolog of EF-G, involved in translocation during eukaryotic translation, not aa-tRNA delivery.

Supporting Evidence

• Structural and biochemical studies confirm EF-Tu’s role in binding aa-tRNA and GTP, delivering the complex to the ribosome with high fidelity.

• Single-molecule fluorescence and molecular dynamics simulations show EF-Tu’s conformational changes coordinate aa-tRNA accommodation.

• EF-Tu is one of the most abundant and conserved proteins in prokaryotes, underscoring its essential role.

Summary Table

Correct Answer

(3) EF-Tu

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Conclusion

The elongation factor responsible for escorting aminoacyl-tRNAs to the ribosome is EF-Tu. It forms a ternary complex with GTP and aa-tRNA, delivers the aa-tRNA to the ribosome’s A site, and ensures high fidelity during translation. Other elongation factors like EF-Ts, EF-G, and eEF-2 have distinct roles unrelated to aa-tRNA delivery.

Correct answer: (3) EF-Tu