Type III CRISPR-Cas loci encode some of the most abundant, yet complex, immune systems of prokaryotes. They are composed of a Cas10 complex that uses an RNA guide to recognize transcripts from bacteriophage and plasmid invaders. Target recognition triggers three activities within this complex: ssDNA degradation, synthesis of cyclic oligoadenylates (cOA) that act as second messengers to activate CARF-domain effectors, and cleavage of target RNA. This review covers recent research in type III CRISPR-Cas systems that looked beyond the activity of the canonical Cas10 complexes towards: (i) ancillary nucleases and understanding how they provide defense by sensing cOA molecules; (ii) ring nucleases and their role in regulating cOA production; and (iii) CRISPR-associated proteases, including the function of the Craspase complex in a transcriptional response to phage infection.

III 型 CRISPR-Cas 位点编码一些最丰富但最复杂的原核生物免疫系统。它们由 Cas10 复合体组成，该复合体使用 RNA 引导来识别噬菌体和质粒入侵者的转录本。目标识别会触发该复合物内的三项活动：ssDNA 降解、作为第二信使激活 CARF 结构域效应器的环状寡腺苷酸 (coA) 的合成以及目标 RNA 的切割。这篇综述涵盖了 III 型 CRISPR-Cas 系统的最新研究，这些研究超越了经典 Cas10 复合物的活性，包括：(i) 辅助核酸酶并了解它们如何通过感知 cOA 分子来提供防御；(ii) 环状核酸酶及其在调节 cOA 产生中的作用；(iii) CRISPR 相关蛋白酶，包括 Craspase 复合物在噬菌体感染转录反应中的功能。