Department of Pathology, Stanford University, Stanford, United States.
Department of Chemical and Systems Biology, Stanford University, Stanford, United States.
Elife. 2017 Aug 17;6:e27601. doi: 10.7554/eLife.27601.
CRISPR-Cas-mediated defense utilizes information stored as spacers in CRISPR arrays to defend against genetic invaders. We define the mode of target interference and role in antiviral defense for two CRISPR-Cas systems in . One system (type I-F) targets DNA. A second system (type III-B) is broadly capable of acquiring spacers in either orientation from RNA and DNA, and exhibits transcription-dependent DNA interference. Examining resistance to phages isolated from Mediterranean seagrass meadows, we found that the type III-B machinery co-opts type I-F CRISPR-RNAs. Sequencing and infectivity assessments of related bacterial and phage strains suggests an 'arms race' in which phage escape from the type I-F system can be overcome through use of type I-F spacers by a horizontally-acquired type III-B system. We propose that the phage-host arms race can drive selection for horizontal uptake and maintenance of promiscuous type III interference modules that supplement existing host type I CRISPR-Cas systems.
CRISPR-Cas 介导的防御利用 CRISPR 阵列中作为间隔物存储的信息来抵御遗传入侵者。我们定义了两种 CRISPR-Cas 系统在 中的靶标干扰模式和抗病毒防御作用。一个系统（I-F 型）靶向 DNA。第二个系统（III-B 型）广泛能够从 RNA 和 DNA 以任意方向获取间隔物，并表现出转录依赖性的 DNA 干扰。通过研究从地中海海草草甸中分离出的噬菌体的抗性，我们发现 III-B 型机制利用 I-F 型 CRISPR-RNAs。对相关细菌和噬菌体菌株的测序和感染性评估表明，在这场“军备竞赛”中，噬菌体可以通过水平获得的 III-B 型系统利用 I-F 型间隔物来逃避 I-F 型系统。我们提出，噬菌体-宿主的军备竞赛可以促进对水平摄取和维持的选择，这些摄取和维持的是混杂的 III 型干扰模块，补充了现有宿主的 I 型 CRISPR-Cas 系统。
