A New Gene Cluster rfe Concerned with the Biosynthesis of Salmonella Lipopolysaccharide

SUMMARY: A new class of rough mutants has been found in both Salmonella montevideo and S. minnesota. The mutants resemble phenotypically rfb mutants, having a complete lipopolysaccharide core but no O-specific material in lipopolysaccharide or as free hapten. The site of these rfe mutations is near the isoleucine and valine gene ilv, and is thus separate from the known lipopolysaccharide gene clusters rfa for the core, rfb for the O-specific side-chains, and rfc for O side-chain polymerization. The function of the rfe gene(s) is not known. It is suggested that they might participate in the utilization of the antigen carrier lipid for lipopolysaccharide synthesis, or that they might regulate the activity of rfb genes. The gene determining phosphorylation of the heptose in the lipopolysaccharide core of S. minnesota was identified as one within the rfa cluster.