TABLE 1 .

Possible directions for future investigation of the proposed model

Question	Reasoning
Is O-unit synthesis regulated?	The proposal that O-unit synthesis is well regulated is based on only a few observations. More-extensive genetic and biochemical studies are needed.
Does WaaL regulate O-unit synthesis?	Additional data are needed to show that WaaL is directly involved in the regulation of O-unit synthesis.
How is regulation achieved?	The model suggests that the regulation proposed most likely involves interactions between multiple proteins, but evidence is lacking. The possibility that regulation may involve transcriptional/translational adjustments will need to be investigated.
Does the proposed protein complex really exist?	We proposed that regulation is achieved by interactions in a multiprotein complex. However, only Wzy and Wzz have been confirmed to interact (23).
How do UndPP-linked O-unit monomers and polymers interact with WaaL ligase?	Can we isolate WaaL in association with its substrates, and can we crystallize WaaL and ultimately view it in its various modes of actions?