[3] UP works in a cycle of phosphorylation and dephosphorylation as the lipid carrier gets used, recycled, and reacts with undecaprenyl phosphate.

[3] UP is involved in transporting peptidoglycan subunits from the cytoplasmic face of the cell membrane to the periplasmic or extracellular surface.

[5][6] The NAG-NAM pentapeptide subunit is then added onto the growing peptidoglycan chain, leaving behind undecaprenyl diphosphate.

The extra phosphate on undecaprenyl diphosphate is cleaved by a pyrophosphatase and UP is then recycled to the cytoplasmic face of the cell membrane.

It is supposed that sugars are assembled into O-antigen subunits directly on UP on the cytoplasmic surface of the cell membrane.

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