Signal Transduction and Cross Regulation in theEscherichia coliPhosphate Regulon by PhoR, CreC, and Acetyl Phosphate

This chapter focuses on the control of the Pho regulon by the signal transduction pathways involving the Pi sensor PhoR, the catabolite regulatory sensor CreC, and acetyl phosphate. It is also poorly understood whether cross regulation by CreC or by acetyl phosphate has a bonafide role in Pho regulon control under certain conditions in normal cells. Therefore, some speculations are provided about the nature of the Pi signal transduction pathway and about the roles of CreC and acetyl phosphate in Pho regulon control. The chapter discusses signal transduction pathways of the Pho regulon. A Pi repression complex may contain all components of the Pst system, PhoU, and PhoR, because all these are required for Pi repression. By testing effects due to ackA and pta mutations, it was shown that activation of the Pho regulon in the absence of both PhoR and CreC requires acetyl phosphate synthesis. Evolutionarily related proteins share sequence similarities at the protein level with other members of the same family. Therefore, sensors are probably structurally and functionally similar to other sensors, and response regulators are probably structurally and functionally similar to other response regulators. The primary control of the Pho regulon involves a signal transduction pathway responsive to the extracellular Pi level.