Type III CRISPR-Cas immunity is widespread in prokaryotes and is generally mediated by multi-subunit effector complexes. These complexes recognize complementary viral transcripts and can activate ancillary immune proteins. Here, we describe a type III-E effector from Candidatus “Scalindua brodae”, called Sb-gRAMP, which is natively encoded by a single gene with several type III domains fused together. This effector uses CRISPR RNA to guide target RNA recognition and cleaves single-stranded RNA at two defined positions six nucleotides apart. Intriguingly, the Sb-gRAMP physically combines with the caspase-like TPR-CHAT peptidase to form the Craspase (CRISPR-guided Caspase) complex, pointing at a potential mechanism of target RNA-induced protease activity to gain viral immunity.

中文翻译：

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gRAMP CRISPR-Cas 效应器是一种与半胱天冬酶样肽酶复合的 RNA 核酸内切酶

III 型 CRISPR-Cas 免疫在原核生物中广泛存在，通常由多亚基效应复合物介导。这些复合物识别互补的病毒转录物并可以激活辅助免疫蛋白。在这里，我们描述了一种来自Candidatus “Scalindua brodae”的 III-E 型效应器，称为Sb -gRAMP，它由单个基因天然编码，其中几个 III 型结构域融合在一起。该效应器使用 CRISPR RNA 来引导目标 RNA 识别，并在相隔 6 个核苷酸的两个确定位置切割单链 RNA。有趣的是，Sb-gRAMP 与 caspase 样 TPR-CHAT 肽酶物理结合形成 Craspase（CRISPR 引导的 Caspase）复合物，指出靶 RNA 诱导的蛋白酶活性以获得病毒免疫的潜在机制。