FIG 2 .

Working model for the regulation of O-unit synthesis. We propose that WaaL sends a feedback signal to WbaP, based on its level of contact with UndPP-linked material in the periplasmic face of the membrane to facilitate the synthesis of more O units. Note that some LPS molecules have only single O units or non-modal-length O-antigen chains, and these are not shown in the figure. Wzx is shown as being involved in bringing the WaaL and WbaP proteins in contact; however, more evidence is required to understand the nature of the proposed molecular machinery.