CRISPR–Cas interference is mediated by Cas effector nucleases that are either components of multisubunit complexes—in class 1 CRISPR–Cas systems—or domains of a single protein—in class 2 systems^1,2,3. Here we show that the subtype III-E effector Cas7-11 is a single-protein effector in the class 1 CRISPR–Cas systems originating from the fusion of a putative Cas11 domain and multiple Cas7 subunits that are derived from subtype III-D. Cas7-11 from Desulfonema ishimotonii (DiCas7-11), when expressed in Escherichia coli, has substantial RNA interference effectivity against mRNAs and bacteriophages. Similar to many class 2 effectors—and unique among class 1 systems—DiCas7-11 processes pre-CRISPR RNA into mature CRISPR RNA (crRNA) and cleaves RNA at positions defined by the target:spacer duplex, without detectable non-specific activity. We engineered Cas7-11 for RNA knockdown and editing in mammalian cells. We show that Cas7-11 has no effects on cell viability, whereas other RNA-targeting tools (such as short hairpin RNAs and Cas13) show substantial cell toxicity^4,5. This study illustrates the evolution of a single-protein effector from multisubunit class 1 effector complexes, expanding our understanding of the diversity of CRISPR systems. Cas7-11 provides the basis for new programmable RNA-targeting tools that are free of collateral activity and cell toxicity.

CRISPR-Cas 干扰由 Cas 效应核酸酶介导，这些核酸酶是多亚基复合物的组成部分（在 1 类 CRISPR-Cas 系统中）或单个蛋白质的结构域 - 在 2 类系统中^1,2,3。在这里，我们显示亚型 III-E 效应子 Cas7-11 是 1 类 CRISPR-Cas 系统中的单蛋白效应子，源自推定的 Cas11 结构域和源自亚型 III-D 的多个 Cas7 亚基的融合。来自Desulfonema ishimotonii 的 Cas7-11 ( Di Cas7-11) 在大肠杆菌中表达时，对 mRNA 和噬菌体具有显着的 RNA 干扰效果。与许多 2 类效应器相似——在 1 类系统中是独一无二的——DiCas7-11 将前 CRISPR RNA 加工成成熟的 CRISPR RNA (crRNA)，并在由目标：间隔双链体定义的位置切割 RNA，没有可检测到的非特异性活性。我们设计了 Cas7-11，用于在哺乳动物细胞中进行 RNA 敲除和编辑。我们表明 Cas7-11 对细胞活力没有影响，而其他 RNA 靶向工具（如短发夹 RNA 和 Cas13）显示出大量的细胞毒性^4,5。本研究说明了单蛋白效应子从多亚基 1 类效应复合物的演变，扩大了我们对 CRISPR 系统多样性的理解。Cas7-11 为没有附带活性和细胞毒性的新型可编程 RNA 靶向工具提供了基础。