BACKGROUND Chlortetracycline (CTC) is one of the commercially important tetracyclines (TCs) family product and is mainly produced by Streptomyces. CTC is still in a great demand due to its broad-spectrum activity against pathogens. Engineering transcriptional control allows the cell to allocate its valuable resources towards protein production and provides an important method for the build-up of desired metabolites. Despite extensive efforts concerning transcriptional regulation for increasing the productivities of TCs, the regulatory mechanisms of the CTC biosynthesis remain poorly understood. RESULTS In this study, the possible regulatory function of CtcS, a potential member of MarR (multiple antibiotic resistance regulator) family of transcriptional regulators in S. aureofaciens F3, was demonstrated. Knockdown of ctcS altered the transcription of several biosynthesis-related genes and reduced the production of tetracycline (TC) and CTC, without obvious effect on morphological differentiation and cell growth. Especially, CtcS directly repressed the transcription of the adjacent divergent gene ctcR (which encodes a putative TC resistance efflux protein). A CtcS-binding site was identified within the promoter region of ctcR by DNase I footprinting and an inverted repeat (5'-CTTGTC-3') composed of two 6-nt half sites in the protected region was found. Moreover, both CTC and TC could attenuate the binding activity of CtcS with target DNA. CONCLUSION ctcS regulated the production of TC and CTC in S. aureofaciens F3 and the overexpression of it could be used as a simple approach for the construction of engineering strain with higher productivity. Meanwhile, CtcS was characterized as a TC- and CTC-responsive MarR family regulator. This study provides a previously unrecognized function of CtcS and will benefit the research on the regulatory machinery of the MarR family regulators.

中文翻译：

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CtcS是MarR家庭调节剂，负责调节金霉素的生物合成。

背景技术四环素（CTC）是商业上重要的四环素（TCs）家族产品之一，主要由链霉菌属（Streptomyces）生产。由于其对病原体的广谱活性，CTC仍然有很大的需求。工程转录控制使细胞能够将其宝贵的资源分配给蛋白质生产，并为积累所需的代谢物提供了重要的方法。尽管在转录调控以增加TC的生产力方面进行了广泛的努力，但对CTC生物合成的调控机制仍然知之甚少。结果在这项研究中，证明了CtcS的可能调节功能，CtcS是金黄色葡萄球菌F3中转录调节因子MarR（多种抗生素抗性调节因子）家族的潜在成员。击倒ctcS改变了几个生物合成相关基因的转录，减少了四环素（TC）和CTC的产生，而对形态分化和细胞生长没有明显影响。特别是，CtcS直接抑制邻近的趋异基因ctcR（其编码一个假定的TC抗性外排蛋白）的转录。通过DNase I足迹在ctcR的启动子区域内鉴定出一个CtcS结合位点，并在保护区内发现了由两个6-nt半位点组成的反向重复序列（5'-CTTGTC-3'）。而且，CTC和TC均可减弱CtcS与靶DNA的结合活性。结论ctcS调节了S中TC和CTC的产生。金黄色葡萄球菌F3及其过表达可作为构建具有较高生产率的工程菌株的简单方法。同时，CtcS被认为是TC和CTC响应的MarR系列调节剂。这项研究提供了CtcS以前无法识别的功能，将有助于对MarR系列调节器的调节机制进行研究。