Molecular cloning and nucleotide sequence analysis of cholera toxin genes of the CtxA- Vibrio cholerae strain Texas Star-SR.

The ctx operons from the Vibrio cholerae El Tor strain 3083 and its CtxA- derivative Texas Star-SR were cloned, and their nucleotide sequences were compared. A single missense mutation in the Texas Star-SR ctxA cistron which results in the substitution of threonine for alanine at position 191 of the 258-amino-acid CtxA precursor was identified. Immunoblot analysis detected the mutant CtxA intracellularly early in the culture cycle but not extracellularly at any growth stage.