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Cotranslational Protein Translocation

Cotranslational Protein Translocation

Translocation of proteins across membranes is an ancient process that occurs even in bacteria and archaebacteria. In fact, the components of the translocation machinery are still conserved between prokaryotes and eukaryotes.
Sec61 channel partners for cotranslational translocation
During cotranslational translocation, the Sec61 channel partners with the signal recognition particle (SRP), the signal recognition particle receptor (SR), and the ribosomes to transport the nascent polypeptide chain...

Ribosomes

Ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that synthesize large quantities of protein—such as secretory cells in the human pancreas—can contain millions of ribosomes.Ribosome Structure and AssemblyRibosomes are composed of ribosomal RNA (rRNA) and proteins. In eukaryotes, rRNA is transcribed from genes in the nucleolus—a part of the nucleus that specializes in ribosome production. Within the...

Ribosomes

Ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that synthesize large quantities of protein—such as secretory cells in the human pancreas—can contain millions of ribosomes.
Ribosome Structure and Assembly
Ribosomes are composed of ribosomal RNA (rRNA) and proteins. In eukaryotes, rRNA is transcribed from genes in the nucleolus—a part of the nucleus that specializes in ribosome production. Within...

Ribosomes

Ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that synthesize large quantities of protein—such as secretory cells in the human pancreas—can contain millions of ribosomes.Ribosome Structure and AssemblyRibosomes are composed of ribosomal RNA (rRNA) and proteins. In eukaryotes, rRNA is transcribed from genes in the nucleolus—a part of the nucleus that specializes in ribosome production. Within the...

Ribosomes

Ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that synthesize large quantities of protein—such as secretory cells in the human pancreas—can contain millions of ribosomes.
Ribosome Structure and Assembly
Ribosomes are composed of ribosomal RNA (rRNA) and proteins. In eukaryotes, rRNA is transcribed from genes in the nucleolus—a part of the nucleus that specializes in ribosome production. Within...

Post-translational Translocation of Proteins to the RER

Post-translational Translocation of Proteins to the RER

A sizable fraction of proteins destined for ER are first synthesized in the cell cytosol and then transported across the ER membrane–a process called post-translational translocation. Similar to cotranslationally translocated proteins, these proteins also use the Sec translocon complex to enter the ER lumen.
Targeting proteins to the ER
Hsp40 and Hsp70 chaperone molecules bind the translated proteins in the cytosol to prevent their folding. The chaperone binding helps to keep the signal...

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Related Experiment Video

Updated: Jul 16, 2026

Dual DNA Rulers to Study the Mechanism of Ribosome Translocation with Single-Nucleotide Resolution

Dual DNA Rulers to Study the Mechanism of Ribosome Translocation with Single-Nucleotide Resolution

Published on: July 8, 2019

Intersubunit movement is required for ribosomal translocation.

Lucas H Horan¹, Harry F Noller

¹Department of Molecular, Cell, and Developmental Biology and Center for Molecular Biology of RNA, University of California, Santa Cruz, CA 95064, USA.

Proceedings of the National Academy of Sciences of the United States of America

|March 16, 2007

Summary

Ribosome subunit movement is essential for protein synthesis. Restricting this movement with a cross-link halted polypeptide synthesis, proving intersubunit motion is required for translocation.

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Last Updated: Jul 16, 2026

Dual DNA Rulers to Study the Mechanism of Ribosome Translocation with Single-Nucleotide Resolution

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Published on: December 16, 2025

Area of Science:

Molecular Biology
Structural Biology
Biochemistry

Background:

Protein synthesis involves the coordinated movement of transfer RNA (tRNA) and messenger RNA (mRNA) through the ribosome.
The ribosome's function is thought to be linked to structural rearrangements, particularly the relative movement between its large (50S) and small (30S) subunits.
Direct experimental evidence demonstrating the necessity of intersubunit movement for translocation has been limited.

Purpose of the Study:

To investigate the role of intersubunit movement in ribosomal translocation during protein synthesis.
To provide direct evidence for the requirement of structural changes between ribosomal subunits for translocation.

Main Methods:

Engineered a disulfide cross-link to physically restrict the movement between the 30S and 50S ribosomal subunits.
Assessed the impact of the cross-link on polypeptide synthesis and translocation activity in vitro.
Utilized reduction of the disulfide bridge to determine if the inhibition of function was reversible.

Main Results:

Cross-linked ribosomes were completely inhibited from carrying out polypeptide synthesis.
The inhibition of protein synthesis was fully reversible upon reduction of the disulfide cross-link.
In vitro assays demonstrated that the cross-linked ribosomes were specifically blocked during elongation factor G-dependent translocation.

Conclusions:

Inter-subunit movement is a mandatory step for ribosomal translocation.
The study provides direct evidence supporting the functional significance of the two-subunit architecture of ribosomes.
These findings elucidate a fundamental mechanism underlying the universal structure and function of ribosomes in protein synthesis.