美国约翰·霍普金斯大学Joshua W. Modell团队发现，一种天然的单向导RNA可重新利用Cas9来自动调节CRISPR-Cas表达。相关论文于2021年1月8日在线发表在《细胞》杂志上。

研究人员证明了在化脓性链球菌CRISPR-Cas系统中，一个长形式的反式激活CRISPR RNA（tracr-L）折叠成一个天然的单一向导，该向导指导Cas9转录抑制其自身的启动子（P cas）。此外，研究人员证明了P cas是关键的调节节点。去抑制会导致针对病毒的免疫速率大幅提高3,000倍；然而，增强免疫力会以增加自身免疫毒性为代价。使用生物信息学分析，研究人员提供了tracrRNA介导的自动调节在II-A型CRISPR-Cas系统中广泛存在的证据。

总之，研究人员揭示了一种通过自然单一向导对CRISPR-Cas系统进行内在调控的新范例，这可能有助于将这些系统频繁地水平转移到尚未发展其自身调控策略的新宿主中。

据悉，CRISPR-Cas系统为原核生物提供了对病毒和质粒的后天免疫力，但是人们对如何调节这些系统以防止自身免疫的了解却很少。

附：英文原文

Title: A natural single-guide RNA repurposes Cas9 to autoregulate CRISPR-Cas expression

Author: Rachael E. Workman, Teja Pammi, Binh T.K. Nguyen, Leonardo W. Graeff, Erika Smith, Suzanne M. Sebald, Marie J. Stoltzfus, Chad W. Euler, Joshua W. Modell

Issue&Volume: 2021-01-08

Abstract: CRISPR-Cas systems provide prokaryotes with acquired immunity against viruses andplasmids, but how these systems are regulated to prevent autoimmunity is poorly understood.Here, we show that in the S. pyogenes CRISPR-Cas system, a long-form transactivating CRISPR RNA (tracr-L) folds into a natural single guide that directs Cas9 to transcriptionally repressits own promoter (Pcas). Further, we demonstrate that Pcas serves as a critical regulatory node. De-repression causes a dramatic 3,000-foldincrease in immunization rates against viruses; however, heightened immunity comesat the cost of increased autoimmune toxicity. Using bioinformatic analyses, we provideevidence that tracrRNA-mediated autoregulation is widespread in type II-A CRISPR-Cas systems. Collectively,we unveil a new paradigm for the intrinsic regulation of CRISPR-Cas systems by naturalsingle guides, which may facilitate the frequent horizontal transfer of these systemsinto new hosts that have not yet evolved their own regulatory strategies.

DOI: 10.1016/j.cell.2020.12.017

Source: https://www.cell.com/cell/fulltext/S0092-8674(20)31687-1