Expression of periplasmic binding proteins for peptide transport is subject to negative regulation by phosphate limitation in Escherichia coli.

It is well recognised that phosphate limitation in Escherichia coli causes enhanced synthesis of a variety of proteins involved in maximising the uptake and utilisation of the available phosphate. In contrast to this situation, we report here that these same conditions repress synthesis of the periplasmic binding proteins for both the oligopeptide (Opp) and dipeptide permeases (Dpp), and of certain other periplasmic proteins. Regulation in the former case is mediated by the Pho regulon; genes controlled by this mechanism lack efficient -35 promoter regions, and instead, an activator protein, PhoB, binds to a specific 'Pho box' sequence, ten bases upstream from a -10 promoter, thereby facilitating binding of RNA polymerase and leading to enhanced transcription. In the latter case, putative Pho boxes can be identified in the promoter regions of opp and dpp (and of other binding proteins), but in these genes they overlap the RNA polymerase binding sites of good promoters. We speculate that this different Pho box location may allow PhoB to act as a repressor of transcription of these genes. The promoter region for the sigma factor, sigma 32, (RpoH) also contains a putative Pho box, implying that it may be involved in the enhanced synthesis and secretion of proteins required under phosphate limitation.