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Biosynthesis of Enterobacterial Common Antigen: The ECA-Trace Phenotype of Salmonella Typhimurium and The Role of the rfe Gene in 08 Side-Chain Synthesis in Escherichia Coli

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Technical Report

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Uniformed Services University Of The Health Sciences Bethesda United States

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Enterobacterial Common Antigen ECA is an outer membrane glycolipid synthesized by all members of the Enterobacteriaceae. The carbohydrate portion of ECA consists of linear heteropolysaccharide chains comprised of trisaccharide repeat units having the structure -3-a-D-Fuc4NAc-1-4-B-D-ManNAcA-1-4-a-D-GlcNAc-1- . The trisaccharide repeat unit is synthesized via the sequential transfer to undecaprenol monophosphate of GlcNAc-1-phosphate, ManNAcA, and Fuc4NAc from UDP-GIcNAc, UDP-ManNAcA, and TDP-Fuc4NAc, respectively. In Salmonella typhimurium the genes involved in the synthesis of ECA are located at two regions on the chromosome- the rfel rff and rib regions. Salmonella typhimurium mutants possessing rfb lesions specifically the rfb A and B genes accumulate ManNAcA -GlcNAc-pyrophosphoryl-undecaprenol lipid II, the dissacharide-linked lipid precursor of ECA, in the inner membrane. These mutants appear to synthesize trace amounts of ECA, and have increased permeability to SDS and other hydrophobic agents. The ECA-trace mutants are unstable, readily acquiring secondary mutations in the rfe or rff loci.

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