FIG 7.

Model of competition for Und-P in E. coli. The PG, ECA, and O-antigen biosynthesis pathways compete for pools of Und-P (red) and UDP-GlcNAc (blue). Interruption of the biosynthesis of ECA, O antigen, or the lipid A core sequesters part of the pool of Und-P and therefore restricts its availability for PG synthesis. Note that the colanic acid biosynthesis pathway, which also utilizes Und-P, is omitted from this illustration because this compound is not appreciably produced under normal growth conditions, though it is highly expressed during stress. Abbreviations: PG, peptidoglycan; UDP-M5, UDP–N-acetylmuramic acid–l-alanine–d-glutamate–meso-diaminopimelic acid–d-alanine–d-alanine; Und-P, undecaprenyl phosphate; GlcNAc, N-acetylglucosamine; Und-PP, undecaprenyl pyrophosphate; ECA, enterobacterial common antigen; LPS, lipopolysaccharide.