Li Yang, Zhao Changbin, Cao Yingqian, Chen Xinhai, Tang Yuanyue, Zhou Xiaohui, Ingmer Hanne, Jiao Xinan, Li Qiuchun
Jiangsu Key Lab of Zoonosis/Jiangsu Co-Innovation Center for Prevention and Control of Important Animal Infectious Diseases and Zoonoses, Yangzhou University, Yangzhou 225100, China.
Joint International Research Laboratory of Agriculture and Agri-Product Safety, Yangzhou University, Yangzhou 225100, China.
Nucleic Acids Res. 2025 Jun 20;53(12). doi: 10.1093/nar/gkaf541.
In prokaryotes, the CRISPR-Cas system provides immunity to invading mobile genetic elements, but its expression is commonly repressed in the absence of phage infection to prevent autoimmunity. How bacteria senses phage infection and activates CRISPR-Cas system are poorly understood. Here, we demonstrate that an essential promoter Pcas, located within the cas1 gene, is the primary promoter driving expression of cas genes encoding the Cas10-Csm interference complex in Staphylococcus aureus type III-A CRISPR-Cas system during phage infection. As a conserved promoter in Staphylococci type III-A CRISPR-Cas system, the Pcas loses its ability to activate cas genes expression when mutated at the C186 site. Importantly, we find that the transcriptional regulator MgrA directly represses type III-A CRISPR-Cas system by interacting with Pcas to prevent autoimmunity. Upon phage infection, MgrA senses oxidative stress and dissociates from the Pcas, alleviating the transcriptional repression and subsequently triggering a robust immunity against phages. Our work provides evidence for the requirement of Pcas within cas1 during type III-A CRISPR-Cas interference stage, and reveals that MgrA-mediated regulation provides an effective mechanism for bacteria to balance avoiding autoimmunityand defending against phages.
在原核生物中，CRISPR-Cas系统为抵御入侵的可移动遗传元件提供免疫保护，但其表达在没有噬菌体感染时通常受到抑制，以防止自身免疫。细菌如何感知噬菌体感染并激活CRISPR-Cas系统目前尚不清楚。在此，我们证明位于cas1基因内的一个关键启动子Pcas是在噬菌体感染期间驱动金黄色葡萄球菌III-A型CRISPR-Cas系统中编码Cas10-Csm干扰复合体的cas基因表达的主要启动子。作为葡萄球菌III-A型CRISPR-Cas系统中的一个保守启动子，Pcas在C186位点发生突变时失去激活cas基因表达的能力。重要的是，我们发现转录调节因子MgrA通过与Pcas相互作用直接抑制III-A型CRISPR-Cas系统，以防止自身免疫。在噬菌体感染时，MgrA感知氧化应激并从Pcas上解离，减轻转录抑制，随后触发对噬菌体的强大免疫反应。我们的工作为III-A型CRISPR-Cas干扰阶段cas1内Pcas的必要性提供了证据，并揭示MgrA介导的调节为细菌平衡避免自身免疫和抵御噬菌体提供了一种有效机制。
