The State Key Laboratory of Microbial Technology, Shandong University, Qingdao, 266237, China.
Shandong Medicinal Biotechnology Center, Shandong Academy of Medical Sciences, Jinan, 250062, China.
Mol Microbiol. 2019 Jul;112(1):29-46. doi: 10.1111/mmi.14252. Epub 2019 Apr 15.
In Streptomyces, GlnR is an activator protein that activates nitrogen-assimilation genes under nitrogen-limiting conditions. However, less is known regarding the regulation of these genes under nitrogen-rich conditions. We determined that the developmental regulator MtrA represses nitrogen-assimilation genes in nitrogen-rich media and that it competes with GlnR for binding to GlnR boxes. The GlnR boxes upstream of multiple nitrogen genes, such as amtB, were confirmed as MtrA binding sites in vitro by electrophoretic mobility shift assays and in vivo by ChIP-qPCR analysis. Transcriptional analysis indicated that, on nutrient-rich medium, MtrA profoundly repressed expression of nitrogen-associated genes, indicating opposing roles for MtrA and GlnR in the control of nitrogen metabolism. Using in vitro and in vivo analysis, we also showed that glnR is itself a direct target of MtrA and that MtrA represses glnR transcription. We further demonstrated functional conservation of MtrA homologues in the recognition of GlnR boxes upstream of nitrogen genes from different actinobacterial species. As mtrA and glnR are widespread among actinomycetes, this mechanism of potential competitive control over nitrogen metabolism genes may be common in this group, adding a major new layer of complexity to the known regulatory network for nitrogen metabolism in Streptomyces and related species.
在链霉菌中，GlnR 是一种激活蛋白，可在氮限制条件下激活氮同化基因。然而，对于富含氮的条件下这些基因的调控知之甚少。我们确定发育调节剂 MtrA 在富含氮的培养基中抑制氮同化基因，并且它与 GlnR 竞争结合 GlnR 盒。多个氮基因（如 amtB）上游的 GlnR 盒被证明是体外电泳迁移率变动分析和体内 ChIP-qPCR 分析中的 MtrA 结合位点。转录分析表明，在营养丰富的培养基上，MtrA 强烈抑制与氮相关的基因的表达，表明 MtrA 和 GlnR 在氮代谢控制中起相反的作用。通过体外和体内分析，我们还表明 glnR 本身是 MtrA 的直接靶标，并且 MtrA 抑制 glnR 的转录。我们进一步证明了来自不同放线菌物种的氮基因上游 GlnR 盒的 MtrA 同源物在识别方面的功能保守性。由于 mtrA 和 glnR 在放线菌中广泛存在，因此这种潜在的氮代谢基因竞争控制机制可能在该类群中很常见，为链霉菌和相关物种中已知的氮代谢调控网络增添了一个主要的新复杂性。
