研究人员报道了来自Candidatus "Scalindua brodae"的III-E型效应器（Sb-GRAMP），它是由一个具有几个III型结构域融合在一起的单一基因自然编码的蛋白。这种效应器使用CRISPR RNA来指导目标RNA的识别，并在相隔6个核苷酸的两个确定的位置切割单链RNA。Sb-GRAMP与类似于caspase的TPR-CHAT肽酶物理结合，形成CRISPR引导的caspase（Craspase）复合物，从而表明目标RNA诱导的蛋白酶活性是获得病毒免疫的潜在机制。
据悉，第三类CRISPR-Cas免疫在原核生物中广泛存在，一般由多亚单位效应复合物介导。这些复合体识别互补的病毒转录本，并能激活辅助免疫蛋白。
附：英文原文
Title: The gRAMP CRISPR-Cas effector is an RNA endonuclease complexed with a caspase-like peptidase
Author: Sam P. B. van Beljouw, Anna C. Haagsma, Alicia Rodríguez-Molina, Daan F. van den Berg, Jochem N. A. Vink, Stan J. J. Brouns
Issue&Volume: 2021-09-17
Abstract: Type III CRISPR-Cas immunity is widespread in prokaryotes and is generally mediated by multisubunit 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” (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. Sb-gRAMP physically combines with the caspase-like TPR-CHAT peptidase to form the CRISPR-guided caspase (Craspase) complex, suggesting a potential mechanism of target RNA–induced protease activity to gain viral immunity.
DOI: abk2718
Source: https://www.science.org/doi/10.1126/science.abk2718