Cohen J S, Wooten J B, Chatterjee C L
Biochemistry. 1981 May 26;20(11):3049-55. doi: 10.1021/bi00514a010.
Medium length (500-200 bp) alternating purine-pyrimidine DNAs were prepared by sonication of synthetic polymers at low temperature. The products, and the hairpin structures derived from them after melting, were sufficiently small for high-resolution 31P NMR studies. Of the five sequences studied, two DNAs, poly(dG-dC).poly(dG-dC) and poly(dA-dU).poly(dA-dU), gave singlet 31P resonances, while three others, poly(dA-dT).poly(dA-dT), poly(dA-br5U).poly(dA-br5U), and poly(dI-dC).poly(dI-dC), exhibited two resolved signals of equal area. This indicates the existence of two distinct alternating phosphodiester backbone conformations for these latter three B-DNAs in solution. Controls of homopolymers, which were also prepared by sonication, showed only singlet 31P resonances. Of the alternating sequences DNAs, only sonicated poly(dG-dC).poly(dG-dC) exhibited a conformational transition to a high salt (greater than 2.5 M) form which exhibited two well-resolved 31P resonances of equal area. This indicates that the high salt form of poly(dG-dC).poly(dG-dC) also has an alternating backbone structure, and it is presumed to be a Z-DNA. These results indicate a general response of the DNA backbone conformation to alternating purine-pyrimidine base sequences but with a degree of sequence and environmental specificity which might have functional genetic significance.
通过在低温下对合成聚合物进行超声处理，制备了中等长度（500 - 200 bp）的交替嘌呤 - 嘧啶DNA。这些产物以及它们在解链后衍生出的发夹结构足够小，适合进行高分辨率的31P NMR研究。在所研究的五个序列中，两种DNA，即聚（dG - dC）·聚（dG - dC）和聚（dA - dU）·聚（dA - dU），给出单重态31P共振信号，而另外三种，聚（dA - dT）·聚（dA - dT）、聚（dA - br5U）·聚（dA - br5U）和聚（dI - dC）·聚（dI - dC），则表现出两个面积相等的分辨信号。这表明后三种B - DNA在溶液中存在两种不同的交替磷酸二酯主链构象。同样通过超声处理制备的均聚物对照仅显示单重态31P共振信号。在交替序列DNA中，只有超声处理的聚（dG - dC）·聚（dG - dC）表现出向高盐（大于2.5 M）形式的构象转变，该高盐形式表现出两个面积相等且分辨良好的31P共振信号。这表明聚（dG - dC）·聚（dG - dC）的高盐形式也具有交替的主链结构，并且推测它是一种Z - DNA。这些结果表明DNA主链构象对交替嘌呤 - 嘧啶碱基序列具有普遍响应，但具有一定程度的序列和环境特异性，这可能具有功能遗传学意义。
