STUDIES OF TOPOISOMERASE II AS TARGET OF ACTION OF ANTICANCER DRUG

DNA嵌入剂和表鬼臼毒素的作用 纯化哺乳动物拓扑异构酶的研究II.DNA嵌入物和 表鬼臼毒素在捕获DNA拓扑异构酶II的同时抑制该酶 由两种酶组成的拓扑异构酶II-DNA DNA裂解复合体 与DNA断裂的5‘-末端共价结合的亚基。 只有在蛋白质被钠变性后才能检测到dna断裂。 十二烷基硫酸酯和蛋白酶K消化。休息时间也会反转 在没有添加核苷酸的情况下添加盐。可裂解的络合物 被嵌入物和表鬼臼毒素困住类似于 拓扑异构酶II DNA断裂-重接反应的中间体。 正是通过这个反应，酶进行了DNA链传递和 DNA拓扑异构化反应。之间的另一种交互模式 拓扑异构酶II-DNA复合体和嵌入物是强制逆转或 解锁可切割的复合体。这种影响已经在很高的时间内观察到 2-甲基-9-羟基椭圆藻的浓度和 双嵌入剂，二叔碳化铵。解锁可裂解的复合体似乎 与DNA结合有关，可能不伴有酶 抑制力。 嵌入剂诱导的拓扑异构酶II作用在细胞内的定位 对核基因组进行了研究。结果发现，某些重复出现的 序列在一段有利的距离内富含 嵌入剂诱导的拓扑异构酶II-DNA连锁。结果是 拓扑异构酶II作用定位的意义 核染色质的环状结构。

The effects of DNA intercalating agents and epipodophyllotoxins are being studied upon purified mammalian topoisomerase II. DNA intercalators and epipodophyllotoxins inhibit DNA topoisomerase II while trapping the enzyme within topoisomerase II-DNA DNA cleavable complexes consit of two enzyme subunits which are covalently bound to the 5'-termini of the DNA break. The DNA breaks can be detected only after protein denaturation by sodium dodecyl sulfate and proteinase K digestion. The breaks also reverse upon salt addition in the absence of added nucleotide. The cleavable complexes trapped by intercalators and epipodophyllotoxins are analogous to intermediates in the DNA breaking-rejoining reaction of topoisomerase II. It is by this reaction that the enzyme carries out DNA strand passage and DNA topoisomerization reaction. Another mode of interaction between topoisomerase II-DNA complexes and intercalator is the forced reversal or unlocking of cleavable complexes. This effect has been observed with high concentrations of 2-methyl-9-hydorxyellipticinium and with the bisintercalator, ditercalinium. The unlocking of cleavable complexes seems to be related to DNA binding and may not be accompanied by enzyme inhibition. The localization of intercalator-induced topoisomerase II action in the nuclear genome was investigated. It was found that certain repeated sequences are enriched at a favored distance from sites of intercalator-induced topoisomerase II-DNA linkage. The results have implications regarding the localization of topoisomerase II action in the loop structure of nuclear chromatin.