Genetic organization of the O7-specific lipopolysaccharide biosynthesis cluster of Escherichia coli VW187 (O7 : K1)

In previous studies the authors cloned and characterized the DNA sequence o f the regions at both ends of the O7-specific lipopolysaccharide (LPS) bios ynthesis cluster of Escherichia coli VW187 (O7:K1), and identified the bios ynthetic genes for dTDP-rhamnose and GDP-mannose, as well as one of the can didate glycosyltransferases. In this work the complete DNA sequence of a 6. 9 kb intervening region is presented, Seven new ORFs were identified. All t he functions required for the synthesis and transfer of the O7 LPS were ass igned on the basis of complementation experiments of transposon insertion o n me oasis or complementation experiments or transposon insertion mutants, and amino acid sequence homology to proteins involved in LPS synthesis of o ther bacteria, Of the seven ORFs, two encoded membrane proteins that were h omologous to the O-antigen translocase (Wzx) and polymerase (Wxy), two were involved in the biosynthesis of dTDP-N-acetylviosamine, and the remaining three showed homologies to sugar transferases, The O antigen chain length r egulator gene wzz was also identified in the vicinity of the O7 polysacchar ide cluster, O7-specific DNA primers were designed and tested for serotypin g of O7 E. coli strains.