The involvement of transport proteins in transcriptional and metabolic regulation.

Transport proteins have sometimes gained secondary regulatory functions that influence gene expression and metabolism. These functions allow communication with the external world via mechanistically distinctive signal transduction pathways. In this brief review we focus on three transport systems in Escherichia coli that control and coordinate carbon, exogenous hexose-phosphate and phosphorous metabolism. The transport proteins that play central roles in these processes are: first, the phosphoenolpyruvate (PEP)-dependent phosphotransferase system (PTS), second, the glucose-6-phosphate receptor, UhpC, and third, the phosphate-specific transporter, PstSABC, respectively. While the PTS participates in multiple complex regulatory processes, three of which are discussed here, UhpC and the Pst transporters exemplify differing strategies.