Break-induced replication (BIR) proceeds via a migrating D-loop for hundreds of kilobases and is highly mutagenic. Previous studies identified long single-stranded (ss) nascent DNA that accumulates during leading strand synthesis to be a target for DNA damage and a primary source of BIR-induced mutagenesis. Here, we describe a new important source of mutagenic ssDNA formed during BIR: the ssDNA template for leading strand BIR synthesis formed during D-loop migration. Specifically, we demonstrate that this D-loop bottom template strand (D-BTS) is susceptible to APOBEC3A (A3A)-induced DNA lesions leading to mutations associated with BIR. Also, we demonstrate that BIR-associated ssDNA promotes an additional type of genetic instability: replication slippage between microhomologies stimulated by inverted DNA repeats. Based on our results we propose that these events are stimulated by both known sources of ssDNA formed during BIR, nascent DNA formed by leading strand synthesis, and the D-BTS that we describe here. Together we report a new source of mutagenesis during BIR that may also be shared by other homologous recombination pathways driven by D-loop repair synthesis.

中文翻译：

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迁移气泡合成通过其模板中的损伤促进诱变

断裂诱导复制 (BIR) 通过迁移 D 环进行数百个碱基，并且具有高度诱变性。以前的研究发现，在前导链合成过程中积累的长单链 (ss) 新生 DNA 是 DNA 损伤的目标，也是 BIR 诱导突变的主要来源。在这里，我们描述了 BIR 期间形成的诱变 ssDNA 的一个新的重要来源：在 D 环迁移期间形成的前导链 BIR 合成的 ssDNA 模板。具体而言，我们证明该 D 环底部模板链 (D-BTS) 易受 APOBEC3A (A3A) 诱导的 DNA 损伤的影响，从而导致与 BIR 相关的突变。此外，我们证明 BIR 相关的 ssDNA 促进了另一种类型的遗传不稳定性：反向 DNA 重复刺激的微同源性之间的复制滑移。根据我们的结果，我们提出这些事件是由 BIR 期间形成的已知 ssDNA 来源、前导链合成形成的新生 DNA 和我们在此描述的 D-BTS 刺激的。我们一起报告了 BIR 期间诱变的新来源，也可能由 D 环修复合成驱动的其他同源重组途径共享。