Capsulation gene loss and 'rescue' mutations during the Cap+ to Cap- transition in Haemophilus influenzae type b.
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.
Brophy
L N
LN
Institute of Molecular Medicine, Oxford University, John Radcliffe Hospital, UK.
Kroll
J S
JS
Ferguson
D J
DJ
Moxon
E R
ER
D016667:Bacterial Capsules / Q000235:genetics*; D015139:Blotting, Southern; D005838:Genotype; D006193:Haemophilus influenzae / Q000235:genetics* / Q000648:ultrastructure; D008854:Microscopy, Electron; D009154:Mutation; D010641:Phenotype; D015183:Restriction Mapping; D014169:Transformation, Bacterial