Salmonella typhimurium mutants defective in UDP-D-galactose:lipopolysaccharide alpha 1,6-D-galactosyltransferase. Structural, immunochemical, and enzymologic studies of rfaB mutants.

The biochemical defect in a class of Salmonella typhimurium mutants (rfaB) defective in biosynthesis of the lipopolysaccharide core is described. Structural, immunochemical and enzymologic studies showed that: (i) the core polysaccharide completely lacked the branch alpha 1,6-D-galactosyl residue of the normal lipopolysaccharide as shown by methylation analysis and 1H nmr spectroscopy; (ii) the mutant lipopolysaccharides acted as acceptors for transfer of D-galactose from UDP-D-galactose into alpha 1,6 linkage to the proximal D-glucosyl residue of the core in a reaction catalyzed by an enzyme activity present in extracts from rfaB+ cells; (iii) the UDP-D-galactose:(glucosyl)lipopolysaccharide alpha 1,6-D-galactosyltransferase activity was absent from extracts of rfaB cells.