Phosphate-dependent regulation of the low- and high-affinity transport systems in the model actinomycete Streptomyces coelicolor

The transport of inorganic phosphate (P(i)) is essential for the growth of all organisms. The metabolism of soil-dwelling Streptomyces species, and their ability to produce antibiotics and other secondary metabolites, are strongly influenced by the availability of phosphate. The transcriptional regulation of the SCO4138 and SCO1845 genes of Streptomyces coelicolor was studied. These genes encode the two putative low-affinity P(i) transporters PitH1 and PitH2, respectively. Expression of these genes and that of the high-affinity transport system pstSCAB follows a sequential pattern in response to phosphate deprivation, as shown by coupling their promoters to a luciferase reporter gene. Expression of pitH2, but not that of pap-pitH1 (a bicistronic transcript), is dependent upon the response regulator PhoP. PhoP binds to specific sequences consisting of direct repeats of 11 nt in the promoter of pitH2, but does not bind to the pap-pitH1 promoter, which lacks these direct repeats for PhoP recognition. The transcription start point of the pitH2 promoter was identified by primer extension analyses, and the structure of the regulatory sequences in the PhoP-protected DNA region was established. It consists of four central direct repeats flanked by two other less conserved repeats. A model for PhoP regulation of this promoter is proposed based on the four promoter DNA-PhoP complexes detected by electrophoretic mobility shift assays and footprinting studies.