Used widely for genome editing, CRISPR-Cas enzymes provide RNA-guided immunity to microbes by targeting foreign nucleic acids for cleavage. We show here that the native activity of CRISPR-Cas12c protects bacteria from phage infection by binding to DNA targets without cleaving them, revealing that antiviral interference can be accomplished without chemical attack on the invader or general metabolic disruption in the host. Biochemical experiments demonstrate that Cas12c is a site-specific ribonuclease capable of generating mature CRISPR RNAs (crRNAs) from precursor transcripts. Furthermore, we find that crRNA maturation is essential for Cas12c-mediated DNA targeting. These crRNAs direct double-stranded DNA binding by Cas12c using a mechanism that precludes DNA cutting. Nevertheless, Cas12c represses transcription and can defend bacteria against lytic bacteriophage infection when targeting an essential phage gene. Together, these results show that Cas12c employs targeted DNA binding to provide antiviral immunity in bacteria, providing a native DNase-free pathway for transient antiviral immunity.

CRISPR-Cas 酶广泛用于基因组编辑，通过靶向外源核酸进行切割，为微生物提供 RNA 引导的免疫。我们在此展示了 CRISPR-Cas12c 的天然活性通过与 DNA 靶标结合而不切割它们来保护细菌免受噬菌体感染，这表明抗病毒干扰可以在不对入侵者进行化学攻击或在宿主中进行一般代谢破坏的情况下完成。生化实验表明，Cas12c 是一种位点特异性核糖核酸酶，能够从前体转录物中生成成熟的 CRISPR RNA (crRNA)。此外，我们发现 crRNA 成熟对于 Cas12c 介导的 DNA 靶向至关重要。这些 crRNA 使用一种阻止 DNA 切割的机制指导 Cas12c 与双链 DNA 结合。尽管如此，当靶向必需的噬菌体基因时，Cas12c 可抑制转录并保护细菌免受裂解性噬菌体感染。总之，这些结果表明，Cas12c 利用靶向 DNA 结合在细菌中提供抗病毒免疫，为瞬时抗病毒免疫提供天然无 DNase 途径。