Nordheim A, Lafer E M, Peck L J, Wang J C, Stollar B D, Rich A
Cell. 1982 Dec;31(2 Pt 1):309-18. doi: 10.1016/0092-8674(82)90124-6.
Negative superhelical coiling of covalently closed DNA plasmids facilitates the formation of left-handed Z-DNA segments. This was demonstrated by binding of antibodies specific for Z-DNA. Plasmid pBR322 and two derivatives from it, pLP32 and pLP014, carrying inserts of alternating CG sequences of 32 bp and 14 bp, respectively, were used. Longer inserts required less negative superhelical density to induce the B-Z transitions. Antibody binding to supercoiled plasmids was also visualized by electron microscopy. Cross-linking of the antibody to the negatively supercoiled plasmid and restriction of the DNA with restriction endonucleases demonstrated that the antibodies combine with the CG insert in pLP32. For pBR322, however, evidence suggests that the antibody combines with a section of DNA containing 14 bases with alternating purine and pyrimidine residues with one residue out of alternation: CACGGGTGCGCATG. These cross-linking studies provide evidence for the binding specificity of the anti-Z-DNA antibodies. On the basis of experimental findings, we have calculated the changes in free energy associated with B-Z transitions in superhelical plasmids.
共价闭合的DNA质粒的负超螺旋盘绕促进左手Z-DNA片段的形成。这通过Z-DNA特异性抗体的结合得以证明。使用了质粒pBR322及其两个衍生物pLP32和pLP014，它们分别携带32 bp和14 bp的交替CG序列插入片段。更长的插入片段诱导B-Z转变所需的负超螺旋密度更低。抗体与超螺旋质粒的结合也通过电子显微镜观察到。抗体与负超螺旋质粒的交联以及用限制性内切酶对DNA的切割表明，抗体与pLP32中的CG插入片段结合。然而，对于pBR322，有证据表明抗体与一段含有14个碱基的DNA结合，这些碱基嘌呤和嘧啶残基交替，其中一个残基不交替：CACGGGTGCGCATG。这些交联研究为抗Z-DNA抗体的结合特异性提供了证据。基于实验结果，我们计算了超螺旋质粒中与B-Z转变相关的自由能变化。
