Lipopolysaccharide O-antigen biosynthesis in Shigella dysenteriae serotype 1: analysis of the plasmid-carried rfp determinant.

The O-antigen polysaccharide of the lipopolysaccharide of Shigella dysenteriae serotype 1 is encoded by determinants located on a 9 kb plasmid (rfp) and on the chromosome near the his locus (rfb). Molecular genetic and biochemical studies of the rfp determinant reported here show that the rfp region contains two genes, rfpA and rfpB, lying in an operon. rfpB was demonstrated to encode a membrane-bound galactosyl-transferase. The low G+C content of rfp DNA suggests that it did not originate in Shigella.