Promoter of the pertussis toxin operon and production of pertussis toxin.

Pertussis toxin (PT), the major virulence factor of Bordetella pertussis, is composed of five different subunits whose genes are organized as an operon. We report the mapping of the promoter region of the PT operon and show that this promoter is only weakly active in Escherichia coli. Bordetella parapertussis and Bordetella bronchiseptica, which do not produce any PT, are shown to have a weaker promoter sequence for this operon and not to produce any detectable PT mRNA. We show that transcription of the PT operon in B. pertussis was constant throughout until the late stationary phase, when transcription significantly decreased. Analysis of the transposon Tn5 mutant BP347 showed that the product of the vir locus was required for transcription of the PT operon. Characterization of the Tn5 mutant BP356 showed that subunit S3 was required for the release of PT into the extracellular medium.