Transcriptional Studies and Regulatory Interactions between thephoR-phoPOperon and thephoU,mtpA, andppkGenes ofStreptomyces lividansTK24

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Abstract
The PhoR/PhoP two-component system ofStreptomyces lividanswas previously shown to allow the growth of the bacteria at low Piconcentrations and to negatively control antibiotic production. The present study focuses on the transcriptional analysis ofphoRandphoP, along with thephoUandmtpAgenes that are transcribed divergently from thephoRPoperon inS. lividans. The effect ofphoR,phoP,phoU, andppkmutations on transcription of these genes was examined under phosphate-replete and phosphate-limited conditions. We demonstrated thatphoRandphoPwere cotranscribed as a leaderless bicistronic transcript cleaved at discrete sites toward the 3′ end ofphoR. In addition,phoPcould also be transcribed alone from a promoter located at the 3′ end ofphoR. ThephoUandmtpAgenes, predicted to encode metal binding proteins, were shown to be transcribed as monocistronic transcripts. The expression ofphoR-phoP,phoP, andphoUwas found to be induced under conditions of Pilimitation inS. lividansTK24. This induction, requiring both PhoR and PhoP, was significantly weaker in thephoUmutant but much stronger in theppkmutant than in the parental strain. The expression ofmtpAwas also shown to be up-regulated when Piwas limiting but independently of PhoR/PhoP. The induction ofmtpAexpression was much stronger in thephoUmutant strain than in the other strains. This study revealed interesting regulatory interactions between the different genes and allowed us to propose putative roles for PhoU and MtpA in the adaptation to phosphate scarcity.

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