EF-G and EF-Tu Structures and Translation Elongation in Bacteria - Elongation Factors EF-Tu, EF-G, and EF-Ts

Sep 21, 2026

Uploaded by Aurelia

Detailed explanation of the protein translation elongation cycle in bacteria, focusing on how the ribosome adds amino acids according to mRNA codons. Describes the coordinated roles of three elongation factors: EF-Tu delivers aminoacylated tRNAs and controls premature hydrolysis; EF-Ts reactivates EF-Tu by GDP-GTP exchange; and EF-G drives translocation of tRNA and mRNA and undergoes GTP hydrolysis. Summarizes the structural features of EF-Tu, including its G domain and conserved nucleotide-recognition motifs.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages843

Reading Time35 h 24 min

AccessFree to download

Elongation cycle overview

Ribosome organization and key elongation factors

Elongation process and factor functions

EF-Tu ternary complex and decoding

Peptidyl transfer and tRNA movement

EF-G translocation and nucleotide hydrolysis

Elongation factor EF-Tu structure

Domain architecture and G domain motifs

e EF-G and EF-Tu Structures and Translation Elongation in Bacteria Poul Nissen and Jens Nyborg University of Aarhus, Aarhus, Denmark The elongation cycle is the productive phase of protein biosynthesis. The genetic message in mRNA is a working transcript of a gene on DNA and it is translated one triplet codon at a time during this phase. Thereby, a speciﬁc amino acid sequence is synthesized and the ﬁnal product represents a functional protein of the living cell. The translation is performed on the ribosome, which is a large complex of ribosomal RNA and ribosomal proteins. The ribosome is organized into two subunits, the large 50S subunit and the small 30S subunit. tRNA molecules provide amino acids for the protein biosynthesis and they are activated by the attachment to tRNA by an aminoacyl bond. During the elongation phase the ribosome is assisted by three elongation factors: (1) elongation factor Tu (EF-Tu), which brings to the ribosome amino-acylated tRNAs (aa-tRNAs) for decoding atthe 30S subunit,(2) elongation factor G (EF-G), which assists the ribosome in translocating mRNA and tRNAs, and (3) elongation factor Ts (EF-Ts), which reactivates EF-Tu by exchanging its cofactor GDP for GTP. EF-Tu and EF-G are both G proteins that are active when GTP is bound as cofactor and inactive when GDP is bound. There is no nucleotide exchange factor for EF-G. The elongation phase and both EF-Tu and EF-G are surprisingly well preserved during evolution, for all living organisms. The proteins corresponding to EF-Ts are more complex in eukaryotes. Elongation The process by which the growing polypeptide on the ribosome is elongated by one amino acid according to the codon on mRNA involves the activities of the three elongation factors: EF-Tu, EF-Ts, and EF-G. EF-Tu in its active complex with GTP interacts with any aa-tRNA and prevents the spontaneous hydrolysis of the ester bond between the amino acid carboxyl acid moiety and the terminal 30-ribose hydroxyls of the tRNA. EF-Tu in this so-called ternary complex interacts with the ribosome in its decoding activity where the correct match between the codon positioned in the decoding center of the 30S subunit and the anti-codon on tRNA is achieved. A signal is sent through as yet unknown routes to the 50S subunit, which reacts by inducing hydrolysis of GTPon EF-Tu at the GTPase center of the ribosome. EF-Tu in its GDP form undergoes a large conformational change and is released from the ternary complex and from the ribosome. The universal 30-CCA end of tRNA is then free to swing into the peptidyl transferase center of the 50S subunit, where the formation of a new peptide bond between the growing polypeptide and the incoming amino acid is performed with the help of catalytic residues of the ribosomal RNA. The released EF-Tu:GDP is reactivated to EF-Tu:GTP with the help of the nucleotide exchange factor EF-Ts. After peptidyl transfer the nascent polypeptide chain is attached to the incoming tRNA, with its anticodon still at the A site of the 30S subunit. It must be shifted to the P site together with the mRNA by exactly one codon. This is performed by EF-G in the translocation stage of elongation, where EF-G pushes the tRNA and the attached codon of the mRNA from the A site into the P site of the 30S subunit. After this the GTP of EF-G is hydrolyzed to GDP at the GTPase center of the ribosome, and EF-G:GDP is released. The high level of GTP in the cell and the relatively low afﬁnity of GDP for EF-G is enough to ensure that EF-G reactivates into EF-G:GTP spontaneously, without the aid of a nucleotide exchange factor. The ribosome has now completed one elongation cycle, and is left with a tRNA with its attached polypeptide in the P site of both the 50S and 30S subunits, and with the previous tRNA pushed into the E (exit) site. The ribosome exposes the next codon in the A site of the 30S subunit and is ready to receive the next cognate tRNA in its complex with EF-Tu:GTP. Elongation

FAQs

What are the three elongation factors involved in bacterial translation elongation?

EF-Tu, EF-Ts, and EF-G. EF-Tu delivers aa-tRNAs and helps decoding; EF-Ts reactivates EF-Tu by GDP-GTP exchange; EF-G promotes translocation of tRNA and mRNA.

How does EF-Tu prevent incorrect or premature chemical reactions during elongation?

In its active GTP-bound ternary complex, EF-Tu interacts with aa-tRNAs and prevents spontaneous hydrolysis of the ester bond within the aminoacyl-tRNA.

What is EF-G’s role in the elongation cycle?

EF-G performs translocation, pushing the tRNA and its codon from the A site into the P site. Its GTP is hydrolyzed to GDP, and EF-G is then released and can be spontaneously reactivated due to cellular nucleotide conditions.

Sep 21, 2026

Uploaded by Aurelia