Degradation of Phage Transcripts by CRISPR-Associated RNases Enables Type III CRISPR-Cas Immunity.
Degradation of Phage Transcripts by CRISPR-Associated RNases Enables Type III CRISPR-Cas Immunity.
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DOI：
10.1016/j.cell.2015.12.053
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发表时间：
2016-02-11
期刊：
影响因子：
64.5
通讯作者：
Marraffini LA
中科院分区：
文献类型：
--
作者：
Jiang W;Samai P;Marraffini LA
III-A型CRISPR-Cas系统使用CRISPR RNA（crRNA）引导的核酸酶保护原核生物免受病毒感染，所述核酸酶执行病毒靶DNA及其转录物的共转录切割。尽管DNA切割对免疫至关重要，但RNA靶向的功能尚不清楚。在这里，我们表明，转录依赖的靶向结果在宿主细胞中的病毒基因组急剧增加时，目标是位于一个晚表达的噬菌体基因。在这种靶向条件下，III-A型RNA酶Csm 3和Csm 6的活性位点的突变导致靶噬菌体mRNA的积累并消除免疫力。当DNA切割效率降低时，还需要Csm 6在突变的噬菌体靶标存在下提供防御。我们的研究结果表明，CRISPR相关RNA酶对噬菌体转录物的降解在导致靶DNA缓慢清除的情况下确保了强大的免疫力。
Type III-A CRISPR-Cas systems defend prokaryotes against viral infection using CRISPR RNA (crRNA)-guided nucleases that perform co-transcriptional cleavage of the viral target DNA and its transcripts. Whereas DNA cleavage is essential for immunity, the function of RNA targeting is unknown. Here we show that transcription-dependent targeting results in a sharp increase of viral genomes in the host cell when the target is located in a late-expressed phage gene. In this targeting condition, mutations in the active sites of the type III-A RNases Csm3 and Csm6 lead to the accumulation of the target phage mRNA and abrogate immunity. Csm6 is also required to provide defense in the presence of mutated phage targets, when DNA cleavage efficiency is reduced. Our results show that the degradation of phage transcripts by CRISPR-associated RNases ensures robust immunity in situations that lead to a slow clearance of the target DNA.