The CRISPR-Cas system owes its utility as a genome-editing tool to its origin as a prokaryotic immune system. The first demonstration of its activity against bacterial viruses (phages) is also the first record of phages evading that immunity ¹ . This evasion can be due to point mutations ¹ , large-scale deletions ² , DNA modifications ³ , or phage-encoded proteins that interfere with the CRISPR-Cas system, known as anti-CRISPRs (Acrs) ⁴ . The latter are of biotechnological interest, as Acrs can serve as off switches for CRISPR-based genome editing ⁵ . Every Acr characterized to date originated from temperate phages, genomic islands, or prophages ^4-8 , and shared properties with the first Acr discovered. Here, with a phage-oriented approach, we have identified an unrelated Acr in a virulent phage of Streptococcus thermophilus. In challenging a S. thermophilus strain CRISPR-immunized against a set of virulent phages, we found one that evaded the CRISPR-encoded immunity >40,000× more often than the others. Through systematic cloning of its genes, we identified an Acr solely responsible for the abolished immunity. We extended our findings by demonstrating activity in another S. thermophilus strain, against unrelated phages, and in another bacterial genus immunized using the heterologous SpCas9 system favoured for genome editing. This Acr completely abolishes SpCas9-mediated immunity in our assays.

中文翻译：

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来自强链球菌噬菌体的抗CRISPR抑制化脓性链球菌Cas9。

CRISPR-Cas系统由于其作为原核免疫系统的起源而被用作基因组编辑工具。它对细菌病毒（噬菌体）活性的第一个证明也是噬菌体逃避免疫力的第一个记录¹。这种逃避可能是由于点突变¹，大规模缺失²，DNA修饰³或干扰CRISPR-Cas系统的噬菌体编码蛋白（称为反CRISPRs（Acrs）^{4）引起的}。后者具有生物技术意义，因为Acrs可以作为基于CRISPR的基因组编辑的关闭开关⁵。迄今为止，每个特征鉴定的Acr都来自温带噬菌体，基因岛或^4-8个噬菌体，并与发现的第一个Acr共享属性。在这里，以噬菌体为导向的方法，我们已经确定了嗜热链球菌的毒性噬菌体中不相关的Acr。在挑战针对一组有毒噬菌体的CRISPR免疫的嗜热链球菌菌株时，我们发现一个比其他物种更能躲避CRISPR编码的免疫> 40,000x。通过系统地克隆其基因，我们确定了Acr完全负责废除免疫力。我们通过证明另一嗜热链球菌菌株对不相关噬菌体的活性，以及​​另一种使用基因组编辑偏爱的SpCas9系统免疫的细菌属的活性，扩展了我们的发现。在我们的测定中，该Acr完全消除了SpCas9介导的免疫力。