AN ASSESSMENT OF THE Z-DNA FORMING POTENTIAL OF ALTERNATING DA-DT STRETCHES IN SUPERCOILED PLASMIDS
AN ASSESSMENT OF THE Z-DNA FORMING POTENTIAL OF ALTERNATING DA-DT STRETCHES IN SUPERCOILED PLASMIDS
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DOI：
10.1021/bi00360a026
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发表时间：
1986-06-17
期刊：
影响因子：
2.9
通讯作者：
RICH, A
中科院分区：
文献类型：
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作者：
ELLISON, MJ;FEIGON, J;RICH, A
通过检查质粒pBR322中包含的序列d(CG)6(TA)4(CG)6的行为，评估了一段交替dA-dT采用左Z形式的能力。通过几种方法分析了该序列中作为负超螺旋度函数的结构转变，包括：(1)通过二维凝胶电泳确定插入物的超螺旋依赖解绕，(2)抗z - dna抗体与插入物的结合，(3)序列对单链特异性内切酶的敏感性，(4)插入物对在d(CG)6段内切的限制性内切酶酶切的敏感性。这些研究表明，在负超卷曲DNA中，插入的两个d(CG)6部分采用Z形式，而中央d(TA)4部分形成带螺旋重复的下缠绕结构，最好近似为介于B形式和Z形式之间。作为负超螺旋度函数的插片展开的统计力学处理提供了将A- t bp从B形式转换为Z形式所需的最小自由能的估计，以及与A- t bp从B形式转换为展开形式相关的自由能。这些结果强烈表明，Z DNA是负超卷曲DNA中d(AT)n延伸的不利结构选择。
The ability of a stretch of alternating dA-dT to adopt the left-handed Z form has been assessed by examining the behavior of the sequence d(CG)6(TA)4(CG)6 contained in the plasmid pBR322. The structural transition occurring within this sequence as a function of negative superhelicity was analyzed by several methods, including (1) the supercoiling-dependent unwinding of the insert as determined by two-dimensional gel electrophoresis, (2) the binding of anti-Z-DNA antibodies to the insert, (3) the sensitivity of the sequence to a single strand specific endonuclease, and (4) the sensitivity of the insert to digestion by a restriciton endonuclease that cuts within the d(CG)6 segments when in the right-handed form. These studies have shown that in negatively supercoiled DNA the two d(CG)6 portions of the insert adopt the Z form, while the central d(TA)4 segment forms an underwound structure with a helical repeat that is best approximated as being intermediate between the B form and the Z form. A statistical mechanical treatment of the unwinding of the insert as a function of negative superhelicity provides an estimate of the minimum free energy required to convert an A-T bp from the B form to the Z form, as well as the free energy associated with the conversion of an A-T bp from the B form to the unwound form. These results strongly indicate that Z DNA is an unfavored structural alternative for stretches of d(AT)n in negatively supercoiled DNA.