Chu Y, Hsu M T
Division of Cardiology, Vanderbilt University School of Medicine, Nashville, TN 37232-2170.
Nucleic Acids Res. 1992 Aug 11;20(15):4033-8. doi: 10.1093/nar/20.15.4033.
We investigated the in vivo effect of ellipticine, a mammalian topoisomeraseII(topoII) inhibitor, on SV40 DNA topology. In contrast to epipodophyllotoxins, ellipticine did not cause significant double stranded cleavage of intracellular SV40 DNA. Furthermore, ellipticine reduced cleavage induced by epipodophyllotoxins, VP16 and VM26. Unexpectedly, ellipticine dramatically increased the superhelical density of a fraction of intracellular SV40 DNA. Several lines of evidence suggest that the formation of this highly supercoiled DNA species (Ih form DNA) is not due to the inhibition of topoII per se, but is the result of intercalation by ellipticine in a subfraction of the intracellular SV40 chromatin followed by the fixation of DNA linking number by a topoisomerase activity. Based on the linking number change and the known unwinding angle of ellipticine, the intercalation density was calculated as one ellipticine molecule per 10-20 bp in the Ih DNA. This result suggests the existence of different populations of intracellular SV40 chromatin with respect to the accessibility to ellipticine intercalation.
我们研究了椭圆玫瑰树碱（一种哺乳动物拓扑异构酶II（topoII）抑制剂）对SV40 DNA拓扑结构的体内效应。与鬼臼毒素不同，椭圆玫瑰树碱不会引起细胞内SV40 DNA的显著双链切割。此外，椭圆玫瑰树碱减少了由鬼臼毒素、VP16和VM26诱导的切割。出乎意料的是，椭圆玫瑰树碱显著增加了细胞内一部分SV40 DNA的超螺旋密度。几条证据表明，这种高度超螺旋DNA物种（Ih型DNA）的形成不是由于topoII本身的抑制，而是椭圆玫瑰树碱插入细胞内SV40染色质的一个亚组分中，随后通过一种拓扑异构酶活性固定DNA连接数的结果。根据连接数变化和椭圆玫瑰树碱已知的解旋角度，计算出Ih DNA中每10 - 20 bp有一个椭圆玫瑰树碱分子的插入密度。这一结果表明，就椭圆玫瑰树碱插入的可及性而言，细胞内SV40染色质存在不同群体。
