Kroeger P E, Rowe T C
Department of Pharmacology and Therapeutics, University of Florida College of Medicine, Gainesville 32610.
Nucleic Acids Res. 1989 Nov 11;17(21):8495-509. doi: 10.1093/nar/17.21.8495.
Topoisomerase I cleavage sites have been mapped in vivo on the Hsp70 heat shock gene of Drosophila melanogaster cells using the drug camptothecin. Topoisomerase I cleavage was only observed when the Hsp70 gene was transcriptionally active. Site-specific single-strand DNA cleavage by topoisomerase I was confined to the transcribed region of the Hsp70 gene and occurred on both the transcribed and nontranscribed DNA strands. A number of the single-strand breaks on the complementary DNA strands occurred in close proximity giving rise to double-stranded DNA breaks. Inhibition of heat-induced Hsp70 transcription by either Actinomycin D (Act D) or 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) inhibited topoisomerase I cleavage except at the 5' and to a lesser extent the 3' end of the gene. Camptothecin (100 microM) inhibited transcription of the Hsp70 gene greater than 95%. These results suggest that topoisomerase I is intimately associated with and has an integral part in Hsp70 gene transcription.
利用喜树碱在体内绘制了果蝇细胞Hsp70热休克基因上的拓扑异构酶I切割位点。仅当Hsp70基因转录活跃时才观察到拓扑异构酶I切割。拓扑异构酶I的位点特异性单链DNA切割局限于Hsp70基因的转录区域，且在转录和非转录的DNA链上均会发生。互补DNA链上的许多单链断裂紧密相邻，导致双链DNA断裂。放线菌素D（Act D）或5,6-二氯-1-β-D-呋喃核糖基苯并咪唑（DRB）对热诱导的Hsp70转录的抑制作用会抑制拓扑异构酶I切割，但基因的5'端以及程度较小的3'端除外。喜树碱（100微摩尔）对Hsp70基因转录的抑制率超过95%。这些结果表明，拓扑异构酶I与Hsp70基因转录密切相关且在其中发挥不可或缺的作用。
