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J. Bacteriol., 01 1995, 312-319, Vol 177, No. 2
PW Annunziato, LF Wright, WF Vann and RP Silver
The K1 capsular polysaccharide, a polymer of sialic acid, is an important
virulence determinant of extraintestinal pathogenic Escherichia coli. The
genes responsible for the synthesis and expression of the polysialic acid
capsule of E. coli K1 are located on the 17-kb kps gene cluster, which is
functionally divided into three regions. Central region 2 encodes proteins
necessary for the synthesis, activation, and polymerization of sialic acid,
while flanking regions 1 and 3 are involved in polymer transport to the
cell surface. In this study, we identified two genes at the proximal end of
region 2, neuD and neuB, which encode proteins with predicted sizes of 22.7
and 38.7 kDa, respectively. Several observations suggest that the neuB gene
encodes sialic acid synthase. EV24, a neuB chromosomal mutant that
expresses a capsule when provided exogenous sialic acid, could be
complemented in trans by the cloned neuB gene. In addition, NeuB has
significant sequence similarity to the product of the cpsB gene of
Neisseria meningitidis group B, which is postulated to encode sialic acid
synthase. We also present data indicating that neuD has an essential role
in K1 polymer production. Cells harboring pSR426, which contains all of
region 2 but lacks region 1 and 3 genes, produce an intracellular polymer.
In contrast, no polymer accumulated in cells carrying a derivative of
pSR426 lacking a functional neuD gene. Unlike strains with mutations in
neuB, however, neuD mutants are not complemented by exogenous sialic acid,
suggesting that NeuD is not involved in sialic acid synthesis.
Additionally, cells harboring a mutation in neuD accumulated sialic acid
and CMP-sialic acid.(ABSTRACT TRUNCATED AT 250 WORDS)
Copyright © 1995, American Society for Microbiology
Nucleotide sequence and genetic analysis of the neuD and neuB genes in region 2 of the polysialic acid gene cluster of Escherichia coli K1
Department of Pediatrics, University of Rochester School of Medicine and Dentistry, New York 14642.
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