Nucleotide sequences within the cholera toxin operon

Nucleotide sequences coding for the N- and C-terminus of the A subunit and the N-terminus of the B subunit of cholera toxin were determined. These results show that the genes for the A and B subunits overlap out of phase by one nucleotide and that each subunit is synthesised as a precursor molecule which is subsequently processes after translation. It is proposed that the synthesis of each subunit is regulated at the translational level. Considerable homology with the heat labile toxin genes of enteropathogenic E.coli was noted.