Phosphate control of the biosynthesis of secondary metabolites in Streptomyces is mediated by the two component system PhoR-PhoP. Linked to the phoR-phoP cluster, and expressed in the opposite orientation, is a phoU-like encoding gene with low identity to the phoU gene of Escherichia coli. Expression of this phoU-like gene is strictly dependent on PhoP activation. We have isolated a PhoU-null mutant and used transcriptomic and RNA-sequencing (RNA-seq) procedures to identify its transcription start site and regulation. RNA-seq studies identified two transcription start sites, one upstream of phoU and the second upstream of the mptA gene. Whereas transcription of PhoU is entirely dependent on PhoP, expression of the downstream mtpA gene is only partially dependent on PhoP activation. The phoU mutant grows more slowly than the parental strain, sporulates poorly and the spores lack pigmentation. Production of actinorhodin and undecylprodigiosin decreased in the phoU mutant, indicating that PhoU has a positive modulating effect on production of these antibiotics. Indeed, transcriptional studies of expression of the actII-ORF4 and redD genes indicated that the PhoU protein activates expression of these antibiotic regulators. Using the glpQ1 promoter as in vivo reporter of the activity of the PHO regulon genes, we observed that expression of glpQ1 is negatively modulated by PhoU. These results were confirmed by reverse transcription-PCR studies of three genes of the PHO regulon; that is, glpQ1, pstS and phoR. In conclusion, PhoU acts as a negative modulator of expression of the PHO regulon genes and as phoU expression is strictly dependent on PhoP activation, this mechanism appears to work as a feed-back control mechanism (self-regulation).The Journal of Antibiotics advance online publication, 1 November 2017; doi:10.1038/ja.2017.130.

中文翻译：

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PHO 调节子的自我控制：PhoP 依赖性蛋白 PhoU 负向控制天蓝色链霉菌中 PHO 调节子基因的表达。


链霉菌次生代谢物生物合成的磷酸盐控制是由双组分系统 PhoR-PhoP 介导的。与 phoR-phoP 簇相连并以相反方向表达的 phoU 样编码基因与大肠杆菌的 phoU 基因具有较低的同一性。该 phoU 样基因的表达严格依赖于 PhoP 的激活。我们分离出一个 PhoU-null 突变体，并使用转录组学和 RNA 测序 (RNA-seq) 程序来鉴定其转录起始位点和调控。 RNA-seq 研究确定了两个转录起始位点，一个位于 phoU 上游，第二个位于 mptA 基因上游。 PhoU 的转录完全依赖于 PhoP，而下游 mtpA 基因的表达仅部分依赖于 PhoP 激活。 phoU 突变体比亲本菌株生长更慢，孢子形成能力差并且孢子缺乏色素沉着。 phoU 突变体中放线菌素和十一烷基灵菌红的产生减少，表明 PhoU 对这些抗生素的产生具有正向调节作用。事实上，actII-ORF4 和 redD 基因表达的转录研究表明，PhoU 蛋白激活这些抗生素调节剂的表达。使用 glpQ1 启动子作为 PHO 调节子基因活性的体内报告基因，我们观察到 glpQ1 的表达受到 PhoU 的负调节。这些结果通过对 PHO 调节子的三个基因的逆转录 PCR 研究得到了证实。即 glpQ1、pstS 和 phoR。总之，PhoU 充当 PHO 调节子基因表达的负调节剂，并且由于 phoU 表达严格依赖于 PhoP 激活，因此该机制似乎作为反馈控制机制（自我调节）发挥作用。《抗生素杂志》提前在线出版，2017 年 11 月 1 日； doi：10.1038/ja.2017.130。