Identification, expression, and DNA sequence of the GDP-mannose biosynthesis genes encoded by the O7 rfb gene cluster of strain VW187 (Escherichia coli O7:K1)

The rfb locus in Escherichia coli is involved in the biosynthesis of O-specific lipopolysaccharide (LPS). Localization of the E. coli gene encoding gluconate-6-phosphate dehydrogenase established the 3' endpoint of the rfb locus. Further sequence analysis of this region revealed the presence of two genes coding for phosphomannomutase and GDP-mannose pyrophosphorylase, enzymes involved in the conversion of mannose-6-phosphate to GDP-mannose, a nucleotide sugar precursor of the O7-specific repeating unit of LPS.