DNA polymerase IV (pol IV) is expressed at increased levels in Escherichia coli cells that suffer DNA damage. In a recent live-cell single-molecule fluorescence microscopy study, we demonstrated that the formation of pol IV foci is strongly recB-dependent in cells treated with the DNA break-inducing antibiotic ciprofloxacin. The results of that study support a model in which pol IV acts to extend D-loop structures during recombinational repair of DNA double-strand breaks. In the present study, we extend upon this work, investigating the UmuD and UmuDʹ proteins as potential modulators of pol IV activity in ciprofloxacin-treated cells. We found that the non-cleavable mutant UmuD(K97A) promotes long-lived association of pol IV with the nucleoid, whereas its cleaved form, UmuDʹ, which accumulates in DNA-damaged cells, reduces binding. The results provide additional support for a model in which UmuD and UmuDʹ directly modulate pol IV-binding to the nucleoid.

DNA 聚合酶 IV (pol IV) 在遭受 DNA 损伤的大肠杆菌细胞中以增加的水平表达。在最近的活细胞单分子荧光显微镜研究中，我们证明 pol IV 病灶的形成是强烈的recB依赖于用 DNA 断裂诱导抗生素环丙沙星处理的细胞。该研究的结果支持一个模型，其中 pol IV 在 DNA 双链断裂的重组修复过程中起到扩展 D 环结构的作用。在本研究中，我们扩展了这项工作，研究了 UmuD 和 UmuDʹ 蛋白作为环丙沙星处理细胞中 pol IV 活性的潜在调节剂。我们发现不可切割的突变体 UmuD(K97A) 促进了 pol IV 与类核的长期结合，而其切割形式 UmuDʹ（在 DNA 损伤的细胞中积累）会降低结合。结果为 UmuD 和 UmuDʹ 直接调节 pol IV 与类核蛋白结合的模型提供了额外的支持。