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Nascent peptide as sole attachment of polysomes to membranes in bacteria
Abstract:
When membrane-polysome complexes from Escherichia coli were treated with puromycin, at various Mg2+ and K+ concentrations, the bulk of the ribosomes were released from the membrane. Moreover, many released ribosomes released ribosomes remained attached to mRNA (pseudopolysomes). These results suggest that ribosomes are attached to the membrane in bacteria solely by their nascent chain. Without a direct attachment the conformational changes associated with chain elongation on the ribosome cannot force the growing chain through the membrane, and so alternative sources of energy for the transfer must be considered.
Insights
Bacterial ribosomes attach to membranes via their nascent polypeptide chains. This attachment is crucial for protein translocation, suggesting alternative energy sources are needed for transfer.
Area of Science:
- Molecular Biology
- Bacterial Physiology
- Protein Synthesis
Background:
- Ribosomes are responsible for protein synthesis.
- In bacteria, ribosomes can associate with the cell membrane.
- The mechanism of ribosome-membrane attachment is not fully understood.
Purpose of the Study:
- To investigate the role of the nascent polypeptide chain in ribosome-membrane attachment in Escherichia coli.
- To determine if ribosomes remain associated with mRNA after release from the membrane.
Main Methods:
- Treatment of membrane-polysome complexes from Escherichia coli with puromycin.
- Varying magnesium (Mg2+) and potassium (K+) ion concentrations.
- Analysis of ribosome-membrane association and mRNA retention.
Main Results:
- The majority of ribosomes detached from the membrane upon puromycin treatment.
- A significant portion of released ribosomes remained attached to messenger RNA (mRNA), forming pseudopolysomes.
- This indicates that the nascent chain is the primary anchor for ribosomes to the membrane.
Conclusions:
- Ribosome attachment to the bacterial membrane is mediated solely by the nascent polypeptide chain.
- The growing polypeptide chain itself does not provide sufficient force for translocation across the membrane.
- Alternative energy sources for protein transfer across the membrane should be explored.