DNA lesions can frequently precede DNA:RNA hybrid accumulation [RNA-seq]

While DNA:RNA hybrids contribute to multiple genomic transactions, their unscheduled formation is a recognized source of DNA lesions. Here, through a suite of systematic screens, we rather observed that a wide range of yeast mutant situations primarily triggering DNA damage actually leads to hybrid accumulation. Focusing on Okazaki fragment processing, we established that genic hybrids can actually form as a consequence of replication-born discontinuities such as unprocessed flaps or unligated Okazaki fragments. Strikingly, such “post-lesion” DNA:RNA hybrids neither detectably contribute to genetic instability, nor disturb gene expression, as opposed to “pre-lesion” hybrids formed upon defective mRNA biogenesis, e.g., THO complex mutants. Post-lesion hybrids similarly arise in distinct genomic instability situations, triggered by pharmacological or genetic manipulation of DNA-dependent processes, both in yeast and human cells. Altogether, our data establish that the accumulation of transcription-born DNA:RNA hybrids can occur as a consequence of various types of natural or pathological DNA lesions, yet do not necessarily aggravate their genotoxicity.尽管DNA:RNA杂交体（DNA:RNA hybrids）参与多种基因组调控过程，但其异常形成是公认的DNA损伤来源。本研究通过一系列系统性筛选实验，反而观察到：多种主要诱发DNA损伤的酵母突变株系，实际上会导致杂交体积累。聚焦于冈崎片段（Okazaki fragment）加工过程，我们证实：基因内的DNA:RNA杂交体实际上可由复制过程产生的不连续结构（如未加工的flap结构或未连接的冈崎片段）所形成。值得注意的是，与mRNA生物发生缺陷（如THO复合物（THO complex）突变）所形成的“损伤前”杂交体不同，这类“损伤后”DNA:RNA杂交体既未被检测到可促进遗传不稳定性，也不会干扰基因表达。此外，在酵母和人类细胞中，由DNA依赖过程的药物处理或遗传操作诱发的多种不同遗传不稳定性场景中，同样会出现这类损伤后杂交体。综上，本研究数据证实：转录衍生的DNA:RNA杂交体的积累，可由多种天然或病理性DNA损伤所导致，但未必会加剧其遗传毒性。