Kennedy A K, Guhathakurta A, Kleckner N, Haniford D B
Department of Biochemistry, University of Western Ontario, London, Canada.
Cell. 1998 Oct 2;95(1):125-34. doi: 10.1016/s0092-8674(00)81788-2.
We present evidence that excision of the nonreplicative transposon Tn10 involves three distinct chemical steps, first-strand nicking, hairpin formation, and hairpin resolution. This three-step mechanism makes it possible for a single protein-active site to cleave two DNA strands of opposite polarity, as appears to be the case in this reaction. We infer the existence of alternating bifunctionality within the active site with suitable modulation of substrate components between steps. DNA double-strand breaks are also made by a "hairpin mechanism" in V(D)J recombination, possibly reflecting the same basic constraints faced in the Tn10 system. Similarities in the basic chemical steps in Tn10 transposition and V(D)J recombination suggest that the V(D)J mechanism may have evolved from a bacterial transposition system.
我们提供的证据表明，非复制型转座子Tn10的切除涉及三个不同的化学步骤，即第一链切口、发夹形成和发夹解析。这种三步机制使得单个蛋白质活性位点能够切割两条极性相反的DNA链，在该反应中似乎就是这种情况。我们推断活性位点内存在交替双功能性，且在步骤之间对底物成分进行了适当调节。在V(D)J重组中，DNA双链断裂也是通过“发夹机制”产生的，这可能反映了Tn10系统面临的相同基本限制。Tn10转座和V(D)J重组中基本化学步骤的相似性表明，V(D)J机制可能是从细菌转座系统进化而来的。
