ROLE OF PHOU IN PHOSPHATE-TRANSPORT AND ALKALINE-PHOSPHATASE REGULATION

The negative regulatory function of PhoU in alkaline phosphatase (AP) synthesis was suggested by the behavior of K10 phoU35 carrying a missense mutation whose product was detected by immunoblotting. To define more clearly the regulatory function of this protein for the synthesis of A.P, we constructed a null mutation. The constitutive synthesis of A.P in this phoU deletion strain confirmed the negative role of PhoU. However, the expression of the PhoU protein from an isopropyl-beta-D-thiogalactopyranoside-inducible promoter had no effect on the repression of AP synthesis. Furthermore, the involvement of PhoU in free-P(i) uptake was demonstrated. These results provide evidence that PhoU participates in P(i) transport and in the regulatory role of the phosphate-specific transport system.