DNA 拓扑异构酶 I 可能导致癌症基因组不稳定。在催化活性过程中，拓扑异构酶 I 形成瞬时中间体拓扑异构酶 I-DNA 裂解复合物 (Top1cc)，以允许链旋转和双链体松弛，从而导致 DNA-RNA 杂合体和微核水平升高。为了理解潜在的机制，我们在 Top1cc 诱导后不久整合了 Top1cc 触发的杂交和 DNA 双链断裂 (DSB) 的基因组数据，揭示了 Top1cc 通过不同的机制提高了杂交水平。 DSB 位于早期复制起始区的高度转录基因处，并与基因 5' 端积累的 RNA 聚合酶 II (RNAPII) 下游的杂交体重叠。损害转录延伸的转录因子 IIS 突变体可能由于回溯而进一步增加了 RNAPII 的积累。此外，Top1ccs 在 G1 晚期或 S 早/中期发生时可以触发微核，但在 S 晚期则不会。由于转录因子 IIS 减弱了微核和转录复制冲突，我们的结果支持 RNAPII 阻滞在 Top1cc 诱导的转录中的作用-导致 DSB 和微核的复制冲突。

DNA topoisomerase I can contribute to cancer genome instability. During catalytic activity, topoisomerase I forms a transient intermediate, topoisomerase I-DNA cleavage complex (Top1cc) to allow strand rotation and duplex relaxation, which can lead to elevated levels of DNA-RNA hybrids and micronuclei. To comprehend the underlying mechanisms, we have integrated genomic data of Top1cc-triggered hybrids and DNA double-strand breaks (DSBs) shortly after Top1cc induction, revealing that Top1ccs increase hybrid levels with different mechanisms. DSBs are at highly transcribed genes in early replicating initiation zones and overlap with hybrids downstream of accumulated RNA polymerase II (RNAPII) at gene 5'-ends. A transcription factor IIS mutant impairing transcription elongation further increased RNAPII accumulation likely due to backtracking. Moreover, Top1ccs can trigger micronuclei when occurring during late G1 or early/mid S, but not during late S. As micronuclei and transcription-replication conflicts are attenuated by transcription factor IIS, our results support a role of RNAPII arrest in Top1cc-induced transcription-replication conflicts leading to DSBs and micronuclei.