Substrate recognition by Dicer elucidated The Dicer protein generates short RNAs from double-stranded RNA (dsRNA) substrates and is critical for RNA interference and antiviral defense. Sinha et al. report structures of a Drosophila Dicer protein that shed light on its two distinct mechanisms for recognizing and cleaving substrates: adenosine triphosphate (ATP)-independent, distributive cleavage of 3′-overhang dsRNAs and ATP-dependent, processive threading of blunt-end dsRNAs. This flexibility might provide invertebrates with the optimization capabilities needed for antiviral defense. Science, this issue p. 329 Structures of a Drosophila Dicer protein reveal two distinct mechanisms recognizing and cleaving double-stranded RNA substrates. Invertebrates rely on Dicer to cleave viral double-stranded RNA (dsRNA), and Drosophila Dicer-2 distinguishes dsRNA substrates by their termini. Blunt termini promote processive cleavage, while 3′ overhanging termini are cleaved distributively. To understand this discrimination, we used cryo–electron microscopy to solve structures of Drosophila Dicer-2 alone and in complex with blunt dsRNA. Whereas the Platform-PAZ domains have been considered the only Dicer domains that bind dsRNA termini, unexpectedly, we found that the helicase domain is required for binding blunt, but not 3′ overhanging, termini. We further showed that blunt dsRNA is locally unwound and threaded through the helicase domain in an adenosine triphosphate–dependent manner. Our studies reveal a previously unrecognized mechanism for optimizing antiviral defense and set the stage for the discovery of helicase-dependent functions in other Dicers.

中文翻译：

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Dicer 使用不同的模块来识别 dsRNA 末端

阐明 Dicer 的底物识别 Dicer 蛋白从双链 RNA (dsRNA) 底物生成短 RNA，对于 RNA 干扰和抗病毒防御至关重要。辛哈等人。报道了果蝇 Dicer 蛋白的结构，揭示了其识别和切割底物的两种不同机制：不依赖三磷酸腺苷 (ATP) 的 3' 突出 dsRNA 的分布式切割和 ATP 依赖性的平端 dsRNA 的持续线程。这种灵活性可能为无脊椎动物提供抗病毒防御所需的优化能力。科学，本期第 14 页。329 果蝇 Dicer 蛋白的结构揭示了识别和切割双链 RNA 底物的两种不同机制。无脊椎动物依靠 Dicer 来切割病毒双链 RNA (dsRNA)，果蝇 Dicer-2 通过末端区分 dsRNA 底物。平末端促进进行性裂解，而 3' 突出末端则进行分配性裂解。为了理解这种区别，我们使用冷冻电子显微镜来解析果蝇 Dicer-2 的单独结构以及与钝 dsRNA 的复合物结构。尽管 Platform-PAZ 结构域被认为是唯一结合 dsRNA 末端的 Dicer 结构域，但出乎意料的是，我们发现解旋酶结构域是结合平末端而非 3' 突出末端所必需的。我们进一步表明，平头 dsRNA 以三磷酸腺苷依赖性方式局部解绕并穿过解旋酶结构域。我们的研究揭示了一种以前未被认识的优化抗病毒防御的机制，并为发现其他 Dicer 中解旋酶依赖性功能奠定了基础。