ROLE OF DNA TOPOISOMERASE-I IN THE TRANSCRIPTION OF SUPERCOILED RIBOSOMAL-RNA GENE
ROLE OF DNA TOPOISOMERASE-I IN THE TRANSCRIPTION OF SUPERCOILED RIBOSOMAL-RNA GENE
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DOI：
10.1073/pnas.84.10.3185
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发表时间：
1987-05-01
影响因子：
11.1
通讯作者：
JACOB, ST
中科院分区：
文献类型：
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作者：
GARG, LC;DIANGELO, S;JACOB, ST
用DEAE-Sephadex柱分离大鼠乳腺腺癌细胞提取物得到的DE-B组分转录线性和超螺旋rRNA基因（rDNA）。已知该部分含有RNA聚合酶I和必需的转录因子，也含有DNA拓扑异构酶I活性。选择性抑制剂喜树碱对这种拓扑异构酶活性的抑制显著减少了超螺旋rDNA的转录，并且在150 μ M的浓度下，喜树碱几乎完全抑制DNA拓扑异构酶I活性和超螺旋rDNA转录。加入外源性小牛胸腺DNA拓扑异构酶I，可恢复提取物转录超螺旋rDNA的能力。喜树碱，即使在500 μ M的浓度下，对线性rDNA的转录也没有显著影响。这些研究表明，DNA拓扑异构酶I对超螺旋rDNA的松弛是其转录所必需的。喜树碱处理后，rRNA合成在体内的优先抑制可能是由于选择性喜树碱抑制DNA拓扑异构酶I活性。
The fraction DE-B obtained by fractionating an extract from rat mammary adenocarcinoma cells on a DEAE-Sephadex column was used for transcribing linear and supercoiled rRNA gene (rDNA). This fraction, which is known to contain RNA polymerase I and essential transcription factors, also contains DNA topoisomerase I activity. Inhibition of this topoisomerase activity by the selective inhibitor camptothecin markedly diminished transcription of supercoiled rDNA, and at a concentration of 150 .mu.M, camptothecin almost completely inhibited DNA topoisomerase I activity and supercoiled rDNA transcription. Addition of exogenous calf thymus DNA topoisomerase I to the sample containing the drug restored the ability of the extract of transcribe supercoiled rDNA. Camptothecin, even at a concentration of 500 .mu.M, had no significant effect on the transcription of linear rDNA. These studies show that relaxation of supercoiled rDNA by DNA topoisomerase I is essential for its transcription. The preferential inhibition of rRNA synthesis in vivo following treatment with camptothecin is probably due to selective camptothecin inhibition of DNA topoisomerase I activity.