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J. Bacteriol., Oct 1995, 5411-5418, Vol 177, No. 19
BR Clarke, D Bronner, WJ Keenleyside, WB Severn, JC Richards and C Whitfield
The 6.6-kb rfb gene cluster from Klebsiella pneumoniae serotype O1
(rfbKpO1) contains six genes whose products are required for the
biosynthesis of a lipopolysaccharide O antigen with the following repeating
unit structure: -->3-beta-D-Galf-1-->3-alpha-D-Galp-1-->(D-
galactan I). rfbFKpO1 is the last gene in the cluster, and its gene product
is required for the initiation of D-galactan I synthesis. Escherichia coli
K-12 strains expressing the RfbFKpO1 polypeptide contain dual
galactopyranosyl and galactofuranosyl transferase activity. This activity
modifies the host lipopolysaccharide core by adding the disaccharide
beta-D-Galf-1-->3-alpha-D-Galp, representing a single repeating unit of
D-galactan I. The formation of the lipopolysaccharide substituted either
with the disaccharide or with authentic polymeric D-galactan I is dependent
on the activity of the Rfe enzyme. Rfe (UDP-GlcpNAc::undecaprenylphosphate
GlcpNAc-1-phosphate transferase) catalyzes the formation of the
lipid-linked biosynthetic intermediate to which galactosyl residues are
transferred during the initial steps of D-galactan I synthesis. The
rfbFKpO1 gene comprises 1,131 nucleotides, and the predicted polypeptide
consists of 373 amino acid residues with a predicted M(r) of 42,600. A
polypeptide with an M(r) of 42,000 was evident in sodium dodecyl
sulfate-polyacrylamide gels when rfbKpO1 was expressed behind the T7
promoter. The carboxy- terminal region of RfbFKpO1 shares similarity with
the carboxy terminus of RfpB, a galactopyranosyl transferase which is
involved in the synthesis of the type 1 O antigen of Shigella dysenteriae.
Copyright © 1995, American Society for Microbiology
Role of Rfe and RfbF in the initiation of biosynthesis of D-galactan I, the lipopolysaccharide O antigen from Klebsiella pneumoniae serotype O1
Department of Microbiology, University of Guelph, Ontario, Canada.
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