title: Genes involved in Haemophilus influenzae type b capsule expression are part of an 18-kilobase tandem duplication.
abstract: Encapsulated Haemophilus influenzae type b produce nonencapsulated variants at high frequency (0.1-0.3%). Cosmid cloning was used to investigate the genetic mechanism responsible for this instability. Analysis of three independently derived cosmid clones showed that the b+ parental strain contains an 18-kilobase tandem duplication of genes involved in type b capsule expression. Loss of one complete copy of the 18-kilobase tandem duplication occurred following transformation of the cosmid clones into Rec+, but not Rec-, Escherichia coli, and in H. influenzae strains that had spontaneously lost capsule expression. These results suggest that high-frequency loss of type b capsule expression is due to rec-dependent recombination between the two copies of the 18-kilobase tandem repeat. This is further supported by our finding that introduction of the H. influenzae rec-1 mutation stabilized type b capsule expression.
mesh_terms: D002874:Chromosome Mapping; D002876:Chromosomes, Bacterial; D003001:Cloning, Molecular; D003360:Cosmids; D004262:DNA Restriction Enzymes; D004926:Escherichia coli / Q000378:metabolism; D005786:Gene Expression Regulation; D005798:Genes, Bacterial; D006193:Haemophilus influenzae / Q000235:genetics* / Q000378:metabolism; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D011938:Rec A Recombinases / Q000502:physiology; D011995:Recombination, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D014169:Transformation, Bacterial
chemical_list: D011135:Polysaccharides, Bacterial; D011938:Rec A Recombinases; D004262:DNA Restriction Enzymes