CRISPR-Cas systems confer adaptive immunity in prokaryotes, facilitating the recognition and destruction of invasive nucleic acids. Type III CRISPR systems comprise large, multisubunit ribonucleoprotein complexes with a catalytic Cas10 subunit. When activated by the detection of foreign RNA, Cas10 generates nucleotide signalling molecules that elicit an immune response by activating ancillary effector proteins. Among these systems, the Bacteroides fragilis type III CRISPR system was recently shown to produce a novel signal molecule, SAM-AMP, by conjugating ATP and SAM. SAM-AMP regulates a membrane effector of the CorA family to provide immunity. Here, we focus on NYN, a ribonuclease encoded within this system, probing its potential involvement in crRNA maturation. Structural modelling and in vitro ribonuclease assays reveal that NYN displays robust sequence-nonspecific, Mn2+-dependent ssRNA-cleavage activity. Our findings suggest a role for NYN in trimming crRNA intermediates into mature crRNAs, which is necessary for type III CRISPR antiviral defence. This study sheds light on the functional relevance of CRISPR-associated NYN proteins and highlights the complexity of CRISPR-mediated defence strategies in bacteria.

中文翻译：

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CRISPR 相关 NYN 核糖核酸酶对 RNA 进行加工


CRISPR-Cas系统赋予原核生物适应性免疫，促进入侵核酸的识别和破坏。 III 型 CRISPR 系统由大型多亚基核糖核蛋白复合物和催化 Cas10 亚基组成。当检测到外来 RNA 后，Cas10 被激活，它会生成核苷酸信号分子，通过激活辅助效应蛋白来引发免疫反应。在这些系统中，脆弱拟杆菌 III 型 CRISPR 系统最近被证明可以通过结合 ATP 和 SAM 产生一种新型信号分子 SAM-AMP。 SAM-AMP 调节 CorA 家族的膜效应器以提供免疫力。在这里，我们重点关注 NYN（一种在该系统中编码的核糖核酸酶），探讨其在 crRNA 成熟中的潜在参与。结构建模和体外核糖核酸酶测定表明，NYN 显示出强大的序列非特异性、Mn2+ 依赖性 ssRNA 切割活性。我们的研究结果表明 NYN 在将 crRNA 中间体修剪成成熟 crRNA 方面发挥着作用，这对于 III 型 CRISPR 抗病毒防御是必需的。这项研究揭示了 CRISPR 相关 NYN 蛋白的功能相关性，并强调了细菌中 CRISPR 介导的防御策略的复杂性。