RADX is a mammalian single-stranded DNA-binding protein that stabilizes telomeres and stalled replication forks. Cellular biology studies have shown that the balance between RADX and Replication Protein A (RPA) is critical for DNA replication integrity. RADX is also a negative regulator of RAD51-mediated homologous recombination at stalled forks. However, the mechanism of RADX acting on DNA and its interactions with RPA and RAD51 are enigmatic. Using single-molecule imaging of the key proteins in vitro, we reveal that RADX condenses ssDNA filaments, even when the ssDNA is coated with RPA at physiological protein ratios. RADX compacts RPA-coated ssDNA filaments via higher-order assemblies that can capture ssDNA in trans. Furthermore, RADX blocks RPA displacement by RAD51 and prevents RAD51 loading on ssDNA. Our results indicate that RADX is an ssDNA condensation protein that inhibits RAD51 filament formation and may antagonize other ssDNA-binding proteins on RPA-coated ssDNA.

中文翻译：

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RADX 浓缩单链 DNA 以对抗 RAD51 加载。

RADX 是一种哺乳动物单链 DNA 结合蛋白，可稳定端粒并停滞复制叉。细胞生物学研究表明，RADX 和复制蛋白 A (RPA) 之间的平衡对于 DNA 复制的完整性至关重要。RADX 也是 RAD51 介导的停滞叉同源重组的负调节因子。然而，RADX 作用于 DNA 的机制及其与 RPA 和 RAD51 的相互作用仍然是个谜。在体外使用关键蛋白质的单分子成像，我们发现 RADX 会浓缩 ssDNA 丝，即使当 ssDNA 以生理蛋白质比例涂有 RPA 时也是如此。RADX 通过可以反式捕获 ssDNA 的高阶组件压缩 RPA 涂层的 ssDNA 丝. 此外，RADX 阻止 RPA 被 RAD51 置换并阻止 RAD51 加载到 ssDNA 上。我们的结果表明 RADX 是一种 ssDNA 缩合蛋白，可抑制 RAD51 丝的形成，并可能拮抗 RPA 包被的 ssDNA 上的其他 ssDNA 结合蛋白。