The bex locus in encapsulated Haemophilus influenzae: a chromosomal region involved in capsule polysaccharide export

Abstract

The nucleotide sequence of a 5.1 kb region in the Haemophilus influenzae type b capsulation locus has been determined and found to contain four open reading frames: bexD, bexC, bexB, and bexA. Comparison of the deduced products of bexC, bexB, and bexA to known proteins, and TnphoA mutagenesis, suggests that they form components of an ATP-driven polysaccharide export apparatus. Furthermore, close sequence similarity between BexA and BexB and products of the kpsT and kpsM genes at the Escherichia coli K5 capsulation locus (Smith et al., 1990--accompanying paper) suggests that capsulation genes in these organisms may have a common ancestry.

The Escherichia coli serA-linked capsule locus and its flanking sequences are polymorphic, genetic evidence for the existence of more than two groups of capsule gene clusters

“…Such a situation exists between the capsule gene clusters of Haemophilus injluenzae, Neisseria meningitidis and E. coli group 11. Despite a lack of nucleotide sequence homology these capsule gene clusters encode a number of functionally homologous proteins (Kroll et al, 1990;Frosch, et al, 1991). Therefore, further genetic analysis is necessary to determine the functional relationships between E. coli group I1 and group 1/11 capsule gene clusters.…”

TnphoA and Its Use in Transposon Mutagenesis

“…These genes (excluding the 3'-end of bexD) were cloned into a plasmid, pLNB24, and mutagenized with TnphoA [6]. Mutants were selected through their production of the blue-colony phenotype on X-phos media and were then examined further [6]. All three of the clones that were looked at were located in the 5' half of bexC, suggesting that its gene product is secreted into the periplasm [6].…”

“…One example of how this approach has been successfully used can be found in the case of bex locus in encapsulated Haemophilus influenzae. A 5.1 kb region in the capsulation locus of H. influenzae was determined using Sanger dideoxy-sequencing and found to contain four open reading frames, called bexd, bexC, bexB, and bexA [6]. These genes (excluding the 3'-end of bexD) were cloned into a plasmid, pLNB24, and mutagenized with TnphoA [6].…”

“…A 5.1 kb region in the capsulation locus of H. influenzae was determined using Sanger dideoxy-sequencing and found to contain four open reading frames, called bexd, bexC, bexB, and bexA [6]. These genes (excluding the 3'-end of bexD) were cloned into a plasmid, pLNB24, and mutagenized with TnphoA [6]. Mutants were selected through their production of the blue-colony phenotype on X-phos media and were then examined further [6].…”

“…Mutants were selected through their production of the blue-colony phenotype on X-phos media and were then examined further [6]. All three of the clones that were looked at were located in the 5' half of bexC, suggesting that its gene product is secreted into the periplasm [6]. Based on this and other information it was postulated that this protein may participate in a pore or carrier mechanism which might assist in the establishment and maintenance of the polysaccharide capsule of H. influenzae, which is a major virulence determinant [6].…”