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Journal of Bacteriology, November 2001, p. 6509-6516, Vol. 183, No. 22
Department of Microbiology and Immunology,
Uniformed Services University of the Health Sciences, Bethesda,
Maryland 20814-4799
Received 22 May 2001/Accepted 14 August 2001
The polysaccharide chains of enterobacterial common antigen (ECA)
are comprised of the trisaccharide repeat unit Fuc4NAc-ManNAcA-GlcNAc, where Fuc4NAc is 4-acetamido-4,6-dideoxy-D-galactose,
ManNAcA is N-acetyl-D-mannosaminuronic acid,
and GlcNAc is N-acetyl-D-glucosamine. Individual trisaccharide repeat units are assembled as
undecaprenyl-linked intermediates in a sequence of reactions that
culminate in the transfer of Fuc4NAc from TDP-Fuc4NAc to
ManNAcA-GlcNAc-pyrophosphorylundecaprenol (lipid II) to yield
Fuc4NAc-ManNAcA-GlcNAc-pyrophosphorylundecaprenol (lipid III), the
donor of trisaccharide repeat units for ECA polysaccharide chain
elongation. Most of the genes known to be involved in ECA assembly are
located in the wec gene cluster located at ca. 85.4 min
on the Escherichia coli chromosome. The available data
suggest that the structural gene for the TDP-Fuc4NAc:lipid II Fuc4NAc transferase also resides in the wec gene cluster;
however, the location of this gene has not been unequivocally defined.
Previous characterization of the nucleotide sequence of the
wec gene cluster in the region between
o416 and wecG revealed that it contained three open reading frames: o74, o204, and
o450. In contrast, the results of experiments described
in the current investigation revealed that it contains only two open
reading frames, o359 and o450. Mutants of
E. coli possessing null mutations in o359
were unable to synthesize ECA, and they accumulated lipid II. In
addition, the in vitro incorporation of [3H]FucNAc from
TDP-[3H]Fuc4NAc into lipid II was not observed in
reaction mixtures using cell extracts obtained from these mutants as a
source of enzyme. The ECA-negative phenotype of these mutants was
complemented by plasmid constructs containing the wild-type
o359 allele, and Fuc4NAc transferase activity was
demonstrated by using cell extracts obtained from the complemented
mutants. Furthermore, partially purified o359 gene
product, expressed as recombinant C-terminal His-tagged protein, was
able to catalyze the in vitro transfer of [3H]Fuc4NAc
from TDP-[3H]Fuc4NAc to lipid II. Our data support the
conclusion that o359 of the wec gene
cluster of E. coli is the structural gene for the
TDP-Fuc4NAc:lipid II Fuc4NAc transferase involved in the synthesis ECA
trisaccharide repeat units.
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.22.6509-6516.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Identification of the Structural Gene for the
TDP-Fuc4NAc:Lipid II Fuc4NAc Transferase Involved in Synthesis of
Enterobacterial Common Antigen in Escherichia coli
K-12
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Uniformed Services University of the
Health Sciences, 4301 Jones Bridge Rd., Bethesda, MD 20814-4799. Phone: (301) 295-3418. Fax: (301) 295-1545. E-mail:
rickp{at}usuhs.mil.
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