An infallible inhibitor of Cas13 CRISPR-Cas13 protects bacterial populations from viral infections by indiscriminately destroying the RNA of the cell and its invader, simultaneously arresting the growth of infected hosts and the spread of the virus. This response is mediated by the Cas13 nuclease, which unleashes massive RNA degradation after recognition of viral transcripts that are complementary to its guide RNA. Meeske et al. discovered AcrVIA1, a viral-encoded inhibitor that binds to Cas13 to occlude the RNA guide and prevent the activation of the nuclease (see the Perspective by Barrangou and Sontheimer). As opposed to inhibitors of DNA-cleaving CRISPR-Cas systems, which require multiple infections to neutralize all Cas nucleases of the host, production of AcrVIA1 by a single virus is sufficient to overcome the CRISPR-Cas13 response. Science, this issue p. 54; see also p. 31 The inhibitor AcrVIA1 completely dismantles type VI CRISPR-Cas immunity even in conditions of multiple targeting or low phage concentration. The CRISPR RNA (crRNA)–guided nuclease Cas13 recognizes complementary viral transcripts to trigger the degradation of both host and viral RNA during the type VI CRISPR-Cas antiviral response. However, how viruses can counteract this immunity is not known. We describe a listeriaphage (ϕLS46) encoding an anti-CRISPR protein (AcrVIA1) that inactivates the type VI-A CRISPR system of Listeria seeligeri. Using genetics, biochemistry, and structural biology, we found that AcrVIA1 interacts with the guide-exposed face of Cas13a, preventing access to the target RNA and the conformational changes required for nuclease activation. Unlike inhibitors of DNA-cleaving Cas nucleases, which cause limited immunosuppression and require multiple infections to bypass CRISPR defenses, a single dose of AcrVIA1 delivered by an individual virion completely dismantles type VI-A CRISPR-mediated immunity.

中文翻译：

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噬菌体编码的抗 CRISPR 能够完全规避 VI-A 型 CRISPR-Cas 免疫


Cas13 的可靠抑制剂 CRISPR-Cas13 通过不加区别地破坏细胞及其入侵者的 RNA，同时阻止受感染宿主的生长和病毒的传播，保护细菌群体免受病毒感染。这种反应是由 Cas13 核酸酶介导的，该酶在识别与其指导 RNA 互补的病毒转录本后，会释放大量 RNA 降解。梅斯克等人。发现了 AcrVIA1，一种病毒编码的抑制剂，它与 Cas13 结合以封闭 RNA 引导并阻止核酸酶的激活（参见 Barrangou 和 Sontheimer 的观点）。 DNA 切割 CRISPR-Cas 系统的抑制剂需要多次感染才能中和宿主的所有 Cas 核酸酶，与此相反，单一病毒产生的 AcrVIA1 足以克服 CRISPR-Cas13 反应。科学，本期第 14 页。 54；另见 p. 31 即使在多重靶向或低噬菌体浓度的条件下，抑制剂 AcrVIA1 也能完全破坏 VI 型 CRISPR-Cas 免疫。 CRISPR RNA (crRNA) 引导的核酸酶 Cas13 识别互补的病毒转录本，在 VI 型 CRISPR-Cas 抗病毒反应期间触发宿主和病毒 RNA 的降解。然而，病毒如何抵消这种免疫力尚不清楚。我们描述了一种编码抗 CRISPR 蛋白 (AcrVIA1) 的李斯特菌噬菌体 (phiLS46)，该蛋白可灭活李斯特菌的 VI-A 型 CRISPR 系统。利用遗传学、生物化学和结构生物学，我们发现 AcrVIA1 与 Cas13a 的引导暴露面相互作用，阻止接近靶 RNA 和核酸酶激活所需的构象变化。 DNA 切割 Cas 核酸酶的抑制剂会产生有限的免疫抑制，并且需要多次感染才能绕过 CRISPR 防御，与此不同的是，单个病毒体递送的单剂量 AcrVIA1 可以完全破坏 VI-A 型 CRISPR 介导的免疫。