THE ASSEMBLY SYSTEM FOR THE OUTER CORE PORTION OF R1-TYPE AND R4-TYPELIPOPOLYSACCHARIDES OF ESCHERICHIA-COLI - THE R1 CORE-SPECIFIC BETA-GLUCOSYLTRANSFERASE PROVIDES A NOVEL ATTACHMENT SITE FOR O-POLYSACCHARIDES

The major core oligosaccharide biosynthesis operons from prototype Esc herichia coli strains displaying R1 and R4 lipopolysaccharide core typ es were polymerase chain reaction-amplified and analyzed. Comparison o f deduced products of the open reading frames between the two regions indicate that all but two share total similarities of 94% or greater. Core oligosaccharide structures resulting from nonpolar insertion muta tions in each gene of the core OS biosynthesis operon in the R1 strain allowed assignment of all of the glycosyltransferase enzymes required for outer core assembly. The difference between the R1 and R4 core ol igosaccharides results from the specificity of the WaaV protein (a bet a 1,3-glucosyltransferase) in R1 and WaaX (a beta 1,4-galactosyltransf erase) in R4. Complementation of the waaV mutant of the R1 prototype s train with the waaX gene of the R4 strain converted the core oligosacc haride from an R1- to an R4-type lipopolysaccharide core molecule. Asi de from generating core oligosaccharide specificity, the unique beta-l inked glucopyranosyl residue of the R1 core plays a crucial role in or ganization of the lipopolysaccharide. This residue provides a novel at tachment site for lipid A-core-linked polysaccharides and distinguishe s the R1-type LPS from existing models for enterobacterial lipopolysac charides.