Kohwi-Shigematsu T, Kohwi Y
Cancer Research Center, La Jolla Cancer Research Foundation, California 92037.
Biochemistry. 1990 Oct 16;29(41):9551-60. doi: 10.1021/bi00493a009.
DNA sequences surrounding the immunoglobulin heavy chain (IgH) enhancer contain negative regulatory elements which are important for the tissue specificity of the enhancer. We have shown that sequences located both 5' and 3' of the enhancer, corresponding to the negative regulatory elements, become stably and uniformly unpaired over an extended length when subjected to torsional stress. These DNA sequences are also included within matrix association regions. The ability of the sequences to assume a stably unpaired conformation was shown by reactivity with chloroacetaldehyde which is specific for unpaired DNA bases, as well as two-dimensional gel electrophoresis of topoisomers. The sequences located 3' of the enhancer induce base unpairing in the direction of the enhancer. This unpaired region progressively expands to include as much as 200 base pairs as the ionic concentration decreases or superhelical density increases. When an ATATAT motif within a negative regulatory element located 3' of the enhancer was mutated, the extensive base-unpairing property was abolished. This base-unpairing property of DNA may be important for negative regulation of gene expression and attachment to the nuclear matrix.
免疫球蛋白重链（IgH）增强子周围的DNA序列包含负调控元件，这些元件对增强子的组织特异性很重要。我们已经表明，增强子5'端和3'端的序列，对应于负调控元件，在受到扭转应力时，会在一段较长的长度上稳定且均匀地解链。这些DNA序列也包含在基质附着区域内。通过与对未配对DNA碱基具有特异性的氯乙醛反应以及拓扑异构体的二维凝胶电泳，表明了这些序列具有形成稳定解链构象的能力。增强子3'端的序列在增强子方向上诱导碱基解链。随着离子浓度降低或超螺旋密度增加，这个未配对区域会逐渐扩展，最多可包含200个碱基对。当增强子3'端的负调控元件内的ATATAT基序发生突变时，广泛的碱基解链特性就会消失。DNA的这种碱基解链特性可能对基因表达的负调控以及与核基质的附着很重要。
