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Membrane Transport Processes Analyzed by a Highly Parallel Nanopore Chip System at Single Protein Resolution
Published on: August 16, 2016
The ribosomal exit tunnel functions as a discriminating gate
Hitoshi Nakatogawa1, Koreaki Ito
1Institute for Virus Research and CREST, Japan Science and Technology Corporation, Kyoto University, Japan.
Cell
|March 15, 2002
Summary
SecM translation stalls due to a specific ribosomal arrest motif. Suppressor mutations in ribosomal components suggest the exit tunnel acts as a gate for nascent protein products.
Area of Science:
- Molecular Biology
- Protein Synthesis
- Ribosome Function
Background:
- SecM is a protein whose translation is regulated by the protein export machinery.
- Nascent protein chains emerging from the ribosome can interact with the ribosomal exit tunnel.
- The precise mechanism of translation arrest and its regulation is not fully understood.
Purpose of the Study:
- To investigate the mechanism of SecM translation arrest.
- To identify the ribosomal components involved in regulating SecM translation.
- To elucidate the role of the ribosomal exit tunnel in nascent protein product discrimination.
Main Methods:
- Site-directed mutagenesis to introduce mutations in SecM and ribosomal components.
- In vitro translation assays to monitor protein synthesis and elongation arrest.
- Analysis of suppressor mutations in 23S ribosomal RNA (rRNA) and ribosomal protein L22.
Main Results:
- A specific sequence motif (FXXXXWIXXXXGIRAGP) in SecM, containing a proline residue, induces elongation arrest within the ribosome.
- Mutations in 23S rRNA and ribosomal protein L22 were identified that suppress this elongation arrest.
- These suppressor mutations map to residues lining the narrowest part of the ribosomal exit tunnel.
Conclusions:
- The identified sequence motif acts as a specific arrest point during translation.
- The narrow constriction of the ribosomal exit tunnel plays a critical role in sensing and responding to nascent polypeptide chains.
- This region of the ribosome functions as a discriminating gate, controlling the passage of proteins based on their sequence and structure.
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