CRISPR-Cas systems provide adaptive immunity in bacteria and archaea by targeting foreign DNA for destruction using CRISPR RNA-guided enzymes. CRISPR immunity begins with integration of foreign sequences into the host CRISPR genomic locus, followed by transcription and maturation of CRISPR RNAs. In a few CRISPR systems, the Cas1 integrase and a Cas6 nuclease are fused to a reverse transcriptase that enables viral sequence acquisition from both DNA and RNA sources. To determine how these components work together, we determined a 3.7 Å resolution cryo-EM structure of a Cas6-RT-Cas1 protein complexed with Cas2, a subunit of the CRISPR integrase. The structure and accompanying mutagenesis experiments provide evidence of bidirectional crosstalk between the Cas1 and RT active sites and unidirectional crosstalk from Cas6 to the Cas1 and RT active sites. Together, these findings suggest regulated structural rearrangements that may coordinate the complex's different enzymatic activities.

中文翻译：

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Cas6-逆转录酶-Cas1-Cas2 CRISPR整合酶复合物活性位点之间的结构协调

CRISPR-Cas系统通过使用CRISPR RNA引导的酶靶向外源DNA进行破坏，从而在细菌和古细菌中提供适应性免疫。CRISPR免疫始于将外源序列整合到宿主CRISPR基因组位点中，然后是CRISPR RNA的转录和成熟。在一些CRISPR系统中，Cas1整合酶和Cas6核酸酶与逆转录酶融合，从而可以从DNA和RNA来源获得病毒序列。为了确定这些组件如何协同工作，我们确定了与CRISPR整合酶的一个亚基Cas2复合的Cas6-RT-Cas1蛋白的3.7Å分辨率冷冻EM结构。结构和伴随的诱变实验提供了Cas1和RT活性位点之间双向串扰以及Cas6与Cas1和RT活性位点之间的单向串扰的证据。