The CRISPR integration complex relies on structural features of DNA to achieve site-selective CRISPR array expansion. Host factor drives the big bend Bacteria have a highly adaptable DNA-detecting and -editing machine called CRISPR-Cas to ward off virus attack. The Cas1-Cas2 integrase, with the help of an accessory protein called IHF (integration host factor), captures foreign DNA motifs into bacterial CRISPR loci. These motifs then act as sensors of any further invaders. By analyzing the integrase complex structure, Wright et al. show how Cas1-Cas2 recognizes the CRISPR array for site-specific integration (see the Perspective by Globus and Qimron). IHF sharply bends DNA, which allows DNA to access two active sites within the integrase complex to ensure sequence specificity for the integration reaction. The features of the CRISPR integrase complex may explain the natural divergence of CRISPR arrays in bacteria and can be exploited for genome-tagging applications. Science, this issue p. 1113; see also p. 1096 CRISPR-Cas systems depend on the Cas1-Cas2 integrase to capture and integrate short foreign DNA fragments into the CRISPR locus, enabling adaptation to new viruses. We present crystal structures of Cas1-Cas2 bound to both donor and target DNA in intermediate and product integration complexes, as well as a cryo–electron microscopy structure of the full CRISPR locus integration complex, including the accessory protein IHF (integration host factor). The structures show unexpectedly that indirect sequence recognition dictates integration site selection by favoring deformation of the repeat and the flanking sequences. IHF binding bends the DNA sharply, bringing an upstream recognition motif into contact with Cas1 to increase both the specificity and efficiency of integration. These results explain how the Cas1-Cas2 CRISPR integrase recognizes a sequence-dependent DNA structure to ensure site-selective CRISPR array expansion during the initial step of bacterial adaptive immunity.

中文翻译：

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CRISPR基因组整合复合物的结构

CRISPR 整合复合物依靠 DNA 的结构特征来实现位点选择性 CRISPR 阵列扩展。宿主因素驱动大弯曲 细菌有一个高度适应性的 DNA 检测和编辑机器，称为 CRISPR-Cas 来抵御病毒攻击。Cas1-Cas2 整合酶在称为 IHF（整合宿主因子）的辅助蛋白的帮助下，将外源 DNA 基序捕获到细菌 CRISPR 基因座中。这些图案然后充当任何进一步入侵者的传感器。通过分析整合酶复合体结构，Wright 等人。展示 Cas1-Cas2 如何识别 CRISPR 阵列以进行特定于位点的整合（参见 Globus 和 Qimron 的观点）。IHF 使 DNA 急剧弯曲，这使 DNA 能够进入整合酶复合物中的两个活性位点，以确保整合反应的序列特异性。CRISPR 整合酶复合物的特征可以解释 CRISPR 阵列在细菌中的自然差异，并可用于基因组标记应用。科学，这个问题 p。1113; 另见第。1096 CRISPR-Cas 系统依赖 Cas1-Cas2 整合酶来捕获短外源 DNA 片段并将其整合到 CRISPR 基因座中，从而能够适应新病毒。我们展示了 Cas1-Cas2 在中间体和产物整合复合物中与供体和靶 DNA 结合的晶体结构，以及完整 CRISPR 基因座整合复合物的冷冻电子显微镜结构，包括辅助蛋白 IHF（整合宿主因子）。该结构出人意料地表明，间接序列识别通过有利于重复和侧翼序列的变形来决定整合位点选择。IHF 结合使 DNA 急剧弯曲，使上游识别基序与 Cas1 接触，以提高整合的特异性和效率。这些结果解释了 Cas1-Cas2 CRISPR 整合酶如何识别序列依赖的 DNA 结构，以确保在细菌适应性免疫的初始步骤中进行位点选择性 CRISPR 阵列扩展。