Fig. 4. Structure and biosynthesis of Kdo-lipid A in E. coliK-12. Only the Kdo and lipid A portions of LPS are required for cell growth. The red symbols indicate the relevant structural genes. A single enzyme catalyses each reaction (1, 2). In almost all sequenced bacteria, the genes encoding the enzymes of lipid A biosynthesis are present in single copy. LpxA and LpxC are the most highly conserved. The structure in the inset is a potent LpxC inhibitor with antibiotic activity comparable to ampicillin (79).