Homologous recombination factors play a crucial role in protecting nascent DNA during DNA replication, but the role of chromatin in this process is largely unknown. Here, we used the bacterial Tus/Ter barrier known to induce a site-specific replication fork stalling in S. cerevisiae. We report that the Set1C subunit Spp1 is recruited behind the stalled replication fork independently of its interaction with Set1. Spp1 chromatin recruitment depends on the interaction of its PHD domain with H3K4me3 parental histones deposited behind the stalled fork. Its recruitment prevents the accumulation of ssDNA at the stalled fork by restricting the access of Exo1. We further show that deleting SPP1 increases the mutation rate upstream of the barrier favoring the accumulation of microdeletions. Finally, we report that Spp1 protects nascent DNA at the Tus/Ter stalled replication fork. We propose that Spp1 limits the remodeling of the fork, which ultimately limits nascent DNA availability to nucleases.

同源重组因子在 DNA 复制过程中保护新生 DNA 方面发挥着至关重要的作用，但染色质在此过程中的作用很大程度上未知。在这里，我们使用已知能在酿酒酵母中诱导位点特异性复制叉停滞的细菌Tus/ Ter屏障。我们报告说，Set1C 亚基 Spp1 在停滞的复制叉后面被招募，独立于其与 Set1 的相互作用。Spp1 染色质的招募取决于其 PHD 结构域与沉积在停滞叉后面的 H3K4me3 亲本组蛋白的相互作用。它的招募通过限制 Exo1 的进入来防止 ssDNA 在停滞的叉处积累。我们进一步表明，删除 SPP 1会增加屏障上游的突变率，有利于微缺失的积累。最后，我们报告 Spp1 保护 Tus/ Ter停滞复制叉处的新生 DNA。我们认为 Spp1 限制了叉的重塑，最终限制了新生 DNA 对核酸酶的可用性。