Members of this family are predicted to be integral membrane proteins with three or four transmembrane spans. They are involved in the synthesis of cell surface polysaccharides. The GtrA family are a subset of this family. GtrA is predicted to be an integral membrane protein with 4 transmembrane spans. It is involved is in O antigen modification by Shigella flexneri bacteriophage X (SfX), but does not determine the specificity of glucosylation. Its function remains unknown, but it may play a role in translocation of undecaprenyl phosphate linked glucose (UndP-Glc) across the cytoplasmic membrane. Another member of this family is a DTDP-glucose-4-keto-6-deoxy-D-glucose reductase, which catalyzes the conversion of dTDP-4-keto-6-deoxy-D-glucose to dTDP-D-fucose, which is involved in the biosynthesis of the serotype-specific polysaccharide antigen of Actinobacillus actinomycetemcomitans Y4 (serotype b). This family also includes the teichoic acid glycosylation protein, GtcA, which is a serotype-specific protein in some Listeria innocua and monocytogenes strains. Its exact function is not known, but it is essential for decoration of cell wall teichoic acids with glucose and galactose.