European Research Institute for the Biology of Ageing, University of Groningen, University Medical Center Groningen, Groningen 9713 AV, The Netherlands.
Proc Natl Acad Sci U S A. 2024 Dec 3;121(49):e2407314121. doi: 10.1073/pnas.2407314121. Epub 2024 Nov 27.
Telomeric DNA sequences are difficult to replicate. Replication forks frequently pause or stall at telomeres, which can lead to telomere truncation and dysfunction. In addition to being at chromosome ends, telomere repeats are also present at internal locations within chromosomes, known as interstitial telomeric sequences (ITSs). These sequences are unstable and prone to triggering gross chromosomal rearrangements (GCRs). In this study, we quantitatively examined the effect of ITSs on the GCR rate in using a genetic assay. We find that the GCR rate increases exponentially with ITS length. This increase can be attributed to the telomere repeat binding protein Rap1 impeding DNA replication and a bias of repairing DNA breaks at or distal to the ITS via de novo telomere addition. Additionally, we performed a genome-wide screen for genes that modulate the rate of ITS-induced GCRs. We find that mutation of core components of the DNA replication machinery leads to an increase in GCRs, but many mutants known to increase the GCR rate in the absence of an ITS do not significantly affect the GCR rate when an ITS is present. We also identified genes that promote the formation of ITS-induced GCRs, including genes with roles in telomere maintenance, nucleotide excision repair, and transcription. Our work thus uncovers multiple mechanisms by which an ITS promotes GCR.
端粒 DNA 序列难以复制。复制叉经常在端粒处暂停或停滞，这可能导致端粒缩短和功能障碍。除了位于染色体末端，端粒重复序列也存在于染色体的内部位置，称为内部端粒序列 (ITSs)。这些序列不稳定，容易引发大规模染色体重排 (GCRs)。在这项研究中，我们使用遗传检测定量研究了 ITS 对 中的 GCR 率的影响。我们发现，GCR 率随 ITS 长度呈指数增长。这种增加可以归因于端粒重复结合蛋白 Rap1 阻碍 DNA 复制，以及通过从头添加端粒来偏向修复 ITS 处或 ITS 远端的 DNA 断裂。此外，我们进行了全基因组筛选，以寻找调节 ITS 诱导的 GCR 率的基因。我们发现，DNA 复制机制的核心成分的突变会导致 GCR 增加，但许多在没有 ITS 的情况下会增加 GCR 率的突变体在存在 ITS 时并不显著影响 GCR 率。我们还确定了促进 ITS 诱导的 GCR 形成的基因，包括在端粒维持、核苷酸切除修复和转录中起作用的基因。因此，我们的工作揭示了多个 ITS 促进 GCR 的机制。
