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Genes for Haemophilus influenzae type b capsule expression are duplicated to form a potentially unstable structure, cap, of directly-repeated chromosomal regions of approximately 17 kb. Capsule-deficient mutants arise in a two-stage process, initiated by rec-dependent reduction of this region from two copies to one. This recombinational event is usually lethal, only about 1/200 surviving to form slow-growing colonies of organisms that continue to synthesize polysaccharide but are defective in its export. A variety of secondary 'rescue' mutations within cap can occur to reduce polysaccharide synthesis and restore normal organism appearance and colony morphology.

Original publication




Journal article


J Gen Microbiol

Publication Date





2571 - 2576


Bacterial Capsules, Blotting, Southern, Genotype, Haemophilus influenzae, Microscopy, Electron, Mutation, Phenotype, Restriction Mapping, Transformation, Bacterial