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Nucleotide sequence of ompV, the gene for a major Vibrio cholerae outer membrane protein
Abstract:
The nucleotide sequence of the ompV gene of Vibrio cholerae was determined. The product of the gene is a 28,000 dalton protein which, after the removal of a 19 amino acid signal sequence, produces a mature outer membrane protein of 26,000 daltons. The cleavage site was determined by amino-terminal amino acid sequencing of the purified mature protein. The DNA upstream of the gene shows the presence of a typical promoter region as judged from the Escherichia coli consensus information; however, the Shine-Dalgarno sequence is associated with a region capable of forming a secondary structure in the mRNA. The formation of this structure would inhibit binding of the mRNA to the ribosome and reduce translation. It is proposed that this structure is recognized by a positive activator in V. cholerae and because of its absence in E. coli ompV is poorly expressed. The distribution of rare codons within ompV suggests that they may serve to slow down the translation of particular domains such that the nascent polypeptide has an opportunity to take up its conformation without interference from the later formed regions. Such a mechanism could aid localization of the protein if export were by a contranslational secretion system.
Insights
The Vibrio cholerae ompV gene encodes an outer membrane protein. Its expression is regulated by mRNA secondary structures and rare codons, potentially influencing protein folding and secretion.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- The ompV gene in Vibrio cholerae encodes an outer membrane protein.
- Understanding gene regulation and protein expression is crucial for bacterial physiology.
Purpose of the Study:
- To determine the nucleotide sequence of the ompV gene in Vibrio cholerae.
- To investigate the factors regulating ompV gene expression and protein maturation.
Main Methods:
- Nucleotide sequencing of the ompV gene.
- Amino-terminal amino acid sequencing of the mature OmpV protein.
- Analysis of promoter regions and mRNA secondary structures.
- Codon usage analysis.
Main Results:
- The ompV gene product is a 28,000-dalton protein, processed to a 26,000-dalton mature outer membrane protein.
- A secondary structure in the ompV mRNA's Shine-Dalgarno region may inhibit translation initiation.
- Rare codons are distributed within ompV, potentially regulating translation speed and protein folding.
- Differences in regulatory elements may explain lower ompV expression in E. coli compared to V. cholerae.
Conclusions:
- The ompV gene's expression is tightly regulated at the translational level.
- mRNA secondary structures and codon usage play roles in OmpV protein production and localization.
- These regulatory mechanisms might be specific to Vibrio cholerae and contribute to its unique outer membrane protein profile.