FIG 1 .

S. enterica group B1 O-antigen synthesis. (A) Biosynthetic pathway. Step 1, transfer by WbaP of galactose-1-phosphate (Gal-P) to Und-P to give UndPP-linked Gal, followed by other glycosyltransferases that build the rest of the O unit sequentially; step 2, Wzx translocation of the O unit across the membrane; step 3, polymerization at the reducing end of a growing UndPP-linked O-unit polymer by Wzy, in effect extending the chain length by one for each cycle; step 4, the ligation reaction catalyzed by WaaL incorporating O antigen into LPS. (B) Genetic map of the O-antigen gene cluster. Pathway genes and products are color coded for each nucleotide sugar precursor. (C) Group B1 O-unit structure (2). Note that the side branch moiety, Abe, shown in blue is missing in Δabe O units.