PIF1 is a 5' to 3' DNA helicase that can unwind double-stranded DNA and disrupt nucleic acid-protein complexes. In Saccharomyces cerevisiae, Pif1 plays important roles in mitochondrial and nuclear genome maintenance, telomere length regulation, unwinding of G-quadruplex structures, and DNA synthesis during break-induced replication. Some, but not all, of these functions are shared with other eukaryotes. To gain insight into the evolutionarily conserved functions of PIF1, we created pif1 null mutants in Drosophila melanogaster and assessed their phenotypes throughout development. We found that pif1 mutant larvae exposed to high concentrations of hydroxyurea, but not other DNA damaging agents, experience reduced survival to adulthood. Embryos lacking PIF1 fail to segregate their chromosomes efficiently during early nuclear divisions, consistent with a defect in DNA replication. Furthermore, loss of the BRCA2 protein, which is required for stabilization of stalled replication forks in metazoans, causes synthetic lethality in third instar larvae lacking either PIF1 or the polymerase delta subunit POL32. Interestingly, pif1 mutants have a reduced ability to synthesize DNA during repair of a double-stranded gap, but only in the absence of POL32. Together, these results support a model in which Drosophila PIF1 functions with POL32 during times of replication stress but acts independently of POL32 to promote synthesis during double-strand gap repair.

中文翻译：

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果蝇 PIF1 解旋酶促进复制应激期间的存活和双链间隙修复期间持续 DNA 合成。

PIF1 是一种 5' 至 3' DNA 解旋酶，可以解开双链 DNA 并破坏核酸-蛋白质复合物。在酿酒酵母中，Pif1 在线粒体和核基因组维护、端粒长度调节、G 四链体结构解旋以及断裂诱导复制过程中的 DNA 合成中发挥重要作用。这些功能中的一些（但不是全部）是与其他真核生物共享的。为了深入了解 PIF1 在进化上保守的功能，我们在果蝇中创建了 pif1 无效突变体，并评估了它们在整个发育过程中的表型。我们发现，暴露于高浓度羟基脲（而非其他 DNA 损伤剂）的 pif1 突变幼虫，其成年期存活率会降低。缺乏 PIF1 的胚胎在早期核分裂过程中无法有效分离染色体，这与 DNA 复制的缺陷一致。此外，后生动物中稳定停滞的复制叉所需的 BRCA2 蛋白的缺失，会导致缺乏 PIF1 或聚合酶 delta 亚基 POL32 的三龄幼虫的合成致死性。有趣的是，pif1 突变体在双链缺口修复过程中合成 DNA 的能力降低，但仅限于缺乏 POL32 的情况。总之，这些结果支持了一个模型，其中果蝇 PIF1 在复制应激期间与 POL32 一起发挥作用，但独立于 POL32 发挥作用，在双链间隙修复期间促进合成。