In response to high amounts of phosphate transport into the cell: a. PhoR is phosphorylated by the phosphate transporter protein Pst b. PhoR binds with PhoB to remove PhoB repression of phosphate regulon genes c. PhoR is exported out of the cell to scavenge phosphate molecules d. PhoU changes conformation to allow PhoR to autophosphorylate e. PhoU keeps PhoR bound to the phosphate transporter protein Pst

PhoU is a membrane protein known to regulate the transport of phosphate (Pi) between cellular compartments. It has been discovered that mutations in this protein cause lethality because the cell becomes incapable of controlling the intracellular levels of Pi, this being toxic for the cell. PhoR is a histidine kinase/phosphatase. When the Pi level is considered to be a limiting factor, PhoR autophosphorylates at a histidine residue and then donates its phosphoryl group to PhoB. On the other hand, when the Pi level is high, this protein removes the phosphoryl group from phospho-PhoB. Finally, the Pst is a signal transduction protein that acts as a transporter capable of switching its conformation during the transport of PI.