FIG. 2.

Primary structure of the B. pertussis S1 pertussis toxin gene showing regions of polymorphism. To date, four ptxA variants have been described and designated ptxA(1), ptxA(2), ptxA(3), and ptxA(4). Dots indicate sequence identity with ptxA(3). Numbers indicate the positions of nucleotides relative to the start codon of AJ245366. Nonsilent mutations are shown in bold and associated amino acid changes are indicated beneath the relevant codons. The figure was adapted with permission from the work of Mooi et al. (15).