Wu J, Liu L F
Department of Pharmacology, UMDNJ-Robert Wood Johnson Medical School, 675 Hoes Lane, Piscataway, NJ 08854, USA.
Nucleic Acids Res. 1997 Nov 1;25(21):4181-6. doi: 10.1093/nar/25.21.4181.
Topoisomerase I (TOP1)-mediated DNA damage induced by camptothecin (CPT) in the presence of active transcription has been studied using purified calf thymus TOP1 and T7 RNA polymerase. CPT-stabilized TOP1 cleavable complexes located on the template strand within the transcribed region were found to be converted into irreversible strand breaks by the elongating RNA polymerase. By contrast, CPT-stabilized TOP1 cleavable complexes located on the non-template strand within the transcribed region was unaffected by the elongating RNA polymerase. Previous studies have demonstrated that the elongating T7 RNA polymerase is arrested by TOP1 cleavable complexes located on the template but not the non-template strand [Bendixen et al ., (1990) Biochemistry , 29, 5613-5619]. Together, these results suggest a model in which collision between the TOP1-cleavable complexes located on the template strand and the elongating RNA polymerase results in transcription arrest and conversion of TOP1 cleavable complexes into 'irreversible' strand breaks. The implication of the transcription collision model in DNA damage and repair, as well as cell killing, is discussed.
利用纯化的小牛胸腺拓扑异构酶I（TOP1）和T7 RNA聚合酶，研究了在活跃转录存在的情况下喜树碱（CPT）诱导的TOP1介导的DNA损伤。发现位于转录区域内模板链上的CPT稳定的TOP1可切割复合物被延伸的RNA聚合酶转化为不可逆的链断裂。相比之下，位于转录区域内非模板链上的CPT稳定的TOP1可切割复合物不受延伸的RNA聚合酶影响。先前的研究表明，延伸的T7 RNA聚合酶会被位于模板而非非模板链上的TOP1可切割复合物所阻滞[本迪克森等人，（1990年）《生物化学》，29，5613 - 5619]。综合这些结果，提出了一个模型，即位于模板链上的TOP1可切割复合物与延伸的RNA聚合酶之间的碰撞导致转录阻滞，并将TOP1可切割复合物转化为“不可逆”的链断裂。讨论了转录碰撞模型在DNA损伤与修复以及细胞杀伤方面的意义。
