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Genetics of cholera toxin
1Center for Vaccine Development, University of Maryland, Baltimore.
The Indian Journal of Medical Research
|July 1, 1992
Summary
Cholera toxin (CT) is produced by Vibrio cholerae and comprises A and B subunits. Gene arrangement and amplification, influenced by RS1 elements, affect CT production in different strains.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Cholera is caused by Vibrio cholerae 01 toxin (CT).
- CT is a protein with A (toxicity) and B (cell binding) subunits, encoded by ctxA and ctxB genes.
- These genes form an operon where ctxA precedes ctxB.
Purpose of the Study:
- To investigate the genetic organization and regulation of the cholera toxin (ctxAB) operon.
- To understand variations in ctxAB gene copy number and arrangement in different Vibrio cholerae strains.
- To identify regulatory elements controlling ctxAB expression.
Main Methods:
- Cloning and sequencing of ctxAB genes.
- Comparative analysis of ctxAB gene copy number and arrangement in various strains.
- Identification of regulatory genes and elements, including the RS1 transposable element.
Main Results:
- Classical strains possess two unlinked ctxAB copies; most others have a single copy.
- Some strains exhibit tandem duplication and amplification of ctxAB, controlled by the RS1 element.
- Multiple genes regulating ctx operon expression have been identified.
- Evidence suggests Vibrio cholerae may produce other toxins besides CT.
Conclusions:
- The ctxAB operon structure and copy number vary significantly among Vibrio cholerae strains.
- Tandem duplication and amplification of ctxAB are mediated by the RS1 element.
- Regulatory mechanisms and potential additional toxins contribute to Vibrio cholerae pathogenicity.