Biosynthesis of enterobacterial common antigen requires dTDPglucose pyrophosphorylase determined by a Salmonella typhimurium rfb gene and a Salmonella montevideo rfe gene.

In group C1 salmonellae, rfe and rff genes linked to the ilv locus specify the synthesis of a glycolipid called the enterobacterial common antigen. In contrast, in group B salmonellae the synthesis requires in addition some of the genes in the rfb cluster, the main genetic determinant of the O side chains of lipopolysaccharide. In an effort to define the biochemical functions of these rfb genes, we looked in Salmonella typhimurium LT2 (group B) for rfb mutants in which the synthesis of both enterobacterial common antigen and the O side chains would be blocked in a manner suppressible by the wild-type rfe cluster of S. montevideo, of group C1. We found one mutant with these characteristics. This rfb mutation affected the activity of dTDPglucose pyrophosphorylase (glucose-1-phosphate thymidylyltransferase, EC 2.7.7.24). Whereas the rfe cluster of S. montevideo contained a gene producing this enzyme activity, there was no evidence for the presence of such a gene in the rfe cluster of group B strains. These results also showed that the synthesis of dTDP-glucose is necessary for the biosynthesis of enterobacterial common antigen; this conclusion fits with the recent demonstration of 4-acetamido-4,6-dideoxy-D-galactose as a component of enterobacterial common antigen (Lugowski et al., Carbohydr. Res. 118:173-181, 1983), because the biosynthesis of the donor of this sugar, dTDP-4-acetamido-4,6-dideoxy-D-galactose, requires dTDPglucose pyrophosphorylase.