The Uhp system uptakes phosphorylated hexose sugars into bacteria.  The system is triggered by phosphorylated hexose sugars on the outside of the cell.  UhpC binds to the phosphorylated hexose, which allows the phosphorylation of UhpB on one of its cytoplasmic histidines.  This facilitates the phosphorylation of an aspartate on UhpA, and the phosphorylated UhpA activates the transcription of UhpT. UhpT then facilitates the transport of the phosphorylated hexose sugars into the cell.