A single enzyme active site that catalyzes multiple reactions is a well-established biochemical theme, but how one nuclease site cleaves both DNA strands of a double helix has not been well understood. In analyzing site-specific DNA cleavage by the mammalian RAG1-RAG2 recombinase, which initiates V(D)J recombination, we find that the active site is reconfigured for the two consecutive reactions and the DNA double helix adopts drastically different structures. For initial nicking of the DNA, a locally unwound and unpaired DNA duplex forms a zipper via alternating interstrand base stacking, rather than melting as generally thought. The second strand cleavage and formation of a hairpin-DNA product requires a global scissor-like movement of protein and DNA, delivering the scissile phosphate into the rearranged active site.

中文翻译：

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在单个活性位点切割反平行DNA链。

催化多种反应的单个酶活性位点是公认的生化主题，但是一个核酸酶位点如何切割双螺旋的两条DNA链尚不清楚。在分析哺乳动物RAG1-RAG2重组酶的位点特异性DNA切割后，该酶会启动V（D）J重组，我们发现该活性位点被重新配置为两个连续的反应，并且DNA双螺旋结构具有截然不同的结构。对于DNA的初始切刻，局部未缠绕和未配对的DNA双链体通过交替的链间碱基堆叠而不是通常认为的熔融形成拉链。第二条链的切割和发夹DNA产物的形成需要蛋白质和DNA的整体剪刀状运动，将易切割的磷酸传递到重排的活性位点。