Liu V F, Weaver D T
Department of Microbiology and Molecular Genetics, Harvard Medical School, Boston, Massachusetts 02115.
Mol Cell Biol. 1993 Dec;13(12):7222-31. doi: 10.1128/mcb.13.12.7222-7231.1993.
Replication protein A (RPA), the trimeric single-stranded DNA-binding protein complex of eukaryotic cells, is important to DNA replication and repair. Phosphorylation of the p34 subunit of RPA is modulated by the cell cycle, occurring during S and G2 but not during G1. The function of phosphorylated p34 remains unknown. We show that RPA p34 phosphorylation is significantly induced by ionizing radiation. The phosphorylated form, p36, is similar if not identical to the phosphorylated S/G2 form. gamma-Irradiation-induced phosphorylation occurs without new protein synthesis and in cells in G1. Mutation of cdc2-type protein kinase phosphorylation sites in p34 eliminates the ionizing radiation response. The gamma-irradiation-induced phosphorylation of RPA p34 is delayed in cells from ataxia telangiectasia, a human inherited disease conferring DNA repair defects and early-onset tumorigenesis. UV-induced phosphorylation of RPA p34 occurs less rapidly than gamma-irradiation-induced phosphorylation but is kinetically similar between ataxia telangiectasia and normal cells. This is the first time that modification of a repair protein, RPA, has been linked with a DNA damage response and suggests that phosphorylation may play a role in regulating DNA repair pathways.
复制蛋白A（RPA）是真核细胞中的三聚体单链DNA结合蛋白复合物，对DNA复制和修复至关重要。RPA的p34亚基的磷酸化受细胞周期调控，在S期和G2期发生，而在G1期不发生。磷酸化的p34的功能仍然未知。我们发现电离辐射可显著诱导RPA p34的磷酸化。磷酸化形式p36与S/G2期磷酸化形式即便不完全相同也极为相似。γ射线照射诱导的磷酸化无需新蛋白质合成，且在G1期细胞中也会发生。p34中cdc2型蛋白激酶磷酸化位点的突变消除了电离辐射反应。在共济失调毛细血管扩张症（一种导致DNA修复缺陷和早发性肿瘤发生的人类遗传性疾病）患者的细胞中，γ射线照射诱导的RPA p34磷酸化出现延迟。紫外线诱导的RPA p34磷酸化比γ射线照射诱导的磷酸化发生得慢，但在共济失调毛细血管扩张症患者和正常细胞之间动力学相似。这是首次将修复蛋白RPA的修饰与DNA损伤反应联系起来，并表明磷酸化可能在调节DNA修复途径中发挥作用。
