多种病毒cas基因拮抗 CRISPR（Acrs）免疫，这一成果由美国华盛顿大学Alexander J. Meeske小组经过不懈努力而取得。2024年9月4日，国际学术期刊《自然》发表了这一成果。

研究人员探究了不同李斯特菌分离物的Acr含量和抑制特异性，它们天然携带四种CRISPR-Cas系统（I-B、II-A、II-C 和 VI-A）。研究发现存在广泛的CRISPR拮抗作用，并追溯到11个由内源性移动元件编码的未知基因家族和4个已知的acr基因家族。其中有两个Acrs与I-B型Cas蛋白具有序列同源性，其中一个组装成有缺陷的干扰复合物。

令人惊讶的是，另外一种I-B型Cas同源物并不影响I型免疫，其通过CRISPR RNA（crRNA）降解抑制了靶向RNA的VI型CRISPR系统。通过探测病毒序列数据库，研究发现了位于假定抗防御基因簇内的大量孤儿cas基因。研究人员验证了一种特别广谱cas3同源物的活性，它能抑制I-B、II-A和VI-A型CRISPR免疫。该观察结果提供了Acr与cas基因共同进化的直接证据，并揭示了具有广谱基因组编辑潜力的新基因。

据了解，原核生物的CRISPR-Cas免疫能力受到抗CRISPRs的威胁，当在噬菌体溶菌周期表达Cas蛋白时或从常驻原生噬菌体或用质粒表达时，抗CRISPRs会抑制Cas蛋白的活性。Acrs通常与特定的同源Cas蛋白结合，因此该抑制作用一般仅针对单一的CRISPR-Cas亚型。此外，尽管acr基因通常位于噬菌体相关基因簇中，但这种抑制机制是如何进化的仍不清楚。

附：英文原文

Title: Diverse viral cas genes antagonize CRISPR immunity

Author: Katz, Mark A., Sawyer, Edith M., Oriolt, Luke, Kozlova, Albina, Williams, Madison C., Margolis, Shally R., Johnson, Matthew, Bondy-Denomy, Joseph, Meeske, Alexander J.

Issue&Volume: 2024-09-04

Abstract: Prokaryotic CRISPR–Cas immunity is subverted by anti-CRISPRs (Acrs), which inhibit Cas protein activities when expressed during the phage lytic cycle or from resident prophages or plasmids1. Acrs often bind to specific cognate Cas proteins, and hence inhibition is typically limited to a single CRISPR–Cas subtype2. Furthermore, although acr genes are frequently organized together in phage-associated gene clusters3, how such inhibitors initially evolve has remained unclear. Here we investigated the Acr content and inhibition specificity of diverse Listeria isolates, which naturally harbour four CRISPR–Cas systems (types I-B, II-A, II-C and VI-A). We observed widespread antagonism of CRISPR, which we traced to 11 previously unknown and 4 known acr gene families encoded by endogenous mobile elements. Among these were two Acrs that possess sequence homology to type I-B Cas proteins, one of which assembles into a defective interference complex. Surprisingly, an additional type I-B Cas homologue did not affect type I immunity, but instead inhibited the RNA-targeting type VI CRISPR system by means of CRISPR RNA (crRNA) degradation. By probing viral sequence databases, we detected abundant orphan cas genes located within putative anti-defence gene clusters. Among them, we verified the activity of a particularly broad-spectrum cas3 homologue that inhibits type I-B, II-A and VI-A CRISPR immunity. Our observations provide direct evidence of Acr evolution by cas gene co-option, and new genes with potential for broad-spectrum control of genome editing technologies.

DOI: 10.1038/s41586-024-07923-x

Source: https://www.nature.com/articles/s41586-024-07923-x