Figure 1. Alleles of pertussis toxin promoter (ptxP) observed worldwide. Bases are numbered –173 to +27 relative to the start of transcription (+1). The region to which 6 dimers of BvgA, the global regulator of B. pertussis virulence genes, bind is shaded. The –10 sequence motif and initiation codon are underlined. The DNA region –370 to –174, not shown here, was devoid of polymorphism. Locations of transcriptional signals and BvgA bindings sites are based on Bartoloni et al. (16).