Figure WN23.5. The capsulation locus cap is a compound transposon (Kroll et al. 1991). (Left) cap gene amplification and reduction by unequal homologous recombination between the direct repeats of IS 1016 (red) that flank the cap genes (blue). The bexA gene is also shown (green). Reversible and irreversible processes are indicated by double- and single-headed arrows, respectively. The level of capsule production (Cap) at each stage is indicated by number of + signs. (Right) cap amplification and reduction typical of most H. influenzae type b strains. The truncated left-hand end of cap is shown, having arisen from a tandem duplication by deletion of 1.2 kb of DNA. Minimum configuration for capsulation is now the Cap⁺⁺ state (Stern et al. 1986). (Reproduced from Fig. 4 of Moxon et al. 1994.)

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