The pstC and phoU genes of pst operon, encoding the phosphate pecific transport system are not regulated by the pho regulon in a phototroph Rhodobacter sphaeroides f. sp. denitrificans

Abstract

The pst operon of Rhodobacter sphaeroides f. sp. denitrificans, which encodes the phosphate-specific transport system, is composed of six genes, pstS, pstC, pstA, pstB, phoU and phoB. Northern blot analysis of the Pst locus showed two different bands, which corresponded to pstS and pstCAB mRNA. Although a phosphate-regulated promoter (Pho box) located upstream of the pstS gene, the upstream sequence of pstC and phoU had no apparent Pho box. The pstC and phoU promoter-driven expression of lacZ activities were reduced to the back ground level in the response to the phosphate limitation. The DNA-binding activity of PhoB was not observed when the organism was grown in the phosphate-limited medium except for the pstS promoter, suggesting that the transcriptional regulation of pstCAB and phoUB is not regulated by pho regulon.