Sam My D, Cascio Duilio, Johnson Reid, Clubb Robert T
Department of Chemistry and Biochemistry and the UCLA-DOE Center for Genomics and Proteomics, University of California, Los Angeles, 405 Hilgard Avenue, Los Angeles, CA 90095-1570, USA.
Acta Crystallogr D Biol Crystallogr. 2003 Jul;59(Pt 7):1238-40. doi: 10.1107/s0907444903008606. Epub 2003 Jun 27.
Bacteriophage lambda uses an elegantly regulated and highly directional site-specific DNA-recombination reaction to integrate and excise its genome. A critical regulator of this process is the phage-encoded excisionase (Xis) protein, which dramatically stimulates excision by orchestrating the assembly of a higher order nucleoprotein structure that excises the prophage. The Xis protein stabilizes this recombination intermediate by substantially altering the trajectory of viral DNA and by cooperatively interacting with the lambda integrase (Int) protein. In an attempt to understand how Xis controls the directionality of bacteriophage lambda recombination, co-crystals of the DNA-binding domain of Xis in complex with its binding site within the P-arm of the phage have been obtained using the hanging-drop vapor-diffusion method. Using sodium acetate as a precipitating reagent, the Xis-DNA complex crystallizes in space group C2, with unit-cell parameters a = 80.2, b = 72.7, c = 38.8 A, beta = 104.1 degrees. These crystals diffract beyond 1.5 A resolution and are well suited for structural analysis using X-ray crystallography.
噬菌体λ利用一种调控精巧且高度定向的位点特异性DNA重组反应来整合和切除其基因组。这一过程的关键调节因子是噬菌体编码的切除酶（Xis）蛋白，它通过精心编排切除原噬菌体的高阶核蛋白结构的组装，极大地刺激了切除反应。Xis蛋白通过显著改变病毒DNA的轨迹并与λ整合酶（Int）蛋白协同相互作用，来稳定这种重组中间体。为了理解Xis如何控制噬菌体λ重组的方向性，采用悬滴气相扩散法获得了Xis的DNA结合结构域与其在噬菌体P臂内的结合位点形成的复合物的共晶体。以醋酸钠作为沉淀剂，Xis-DNA复合物在空间群C2中结晶，晶胞参数为a = 80.2，b = 72.7，c = 38.8 Å，β = 104.1°。这些晶体的衍射分辨率超过1.5 Å，非常适合使用X射线晶体学进行结构分析。
