Yeast telomere capping protein Stn1 overrides DNA replication control through the S phase checkpoint
Yeast telomere capping protein Stn1 overrides DNA replication control through the S phase checkpoint
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DOI：
10.1073/pnas.0812605106
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发表时间：
2009-02-17
影响因子：
11.1
通讯作者：
Nugent, Constance I.
中科院分区：
文献类型：
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作者：
Gasparyan, Hovik J.;Xu, Ling;Nugent, Constance I.
端粒的完整性通过末端保护蛋白来维持，末端保护蛋白阻断核酸酶降解并防止端粒被识别为DNA断裂。虽然不太清楚，末端保护蛋白也可能在促进端粒复制中发挥作用。在这里，我们表明，过量生产（OP）的酵母端粒加帽蛋白Stn1使细胞高度敏感的复制抑制剂的羟基脲（HU）和甲基甲烷磺酸盐（MMS）。出乎意料的是，这种敏感性对应于Stn1OP阻断S期检查点的大多数方面（如果不是全部的话）。检查点激酶Rad53在Stn1 OP细胞中以正常时间磷酸化，表明Stn1不干扰激活检查点所涉及的信号步骤。Stn1在端粒完整性中的部分作用是通过DNA聚合酶α的Pol12亚基（Pol α）介导的。我们发现，过度产生的Stn1通常与HU处理和未处理细胞中的染色体相关，并且值得注意的是，Stn1染色体结合和OP检查点缺陷在pol12突变体中被拯救。我们建议Stn1通常促进端粒的Pol α活性，但当过度产生时，可以通过Pol12招募到非端粒位点。在复制应激期间，错误定位的Stn 1可能以干扰控制复制叉完整性的Rad53效应器机制的方式不适当地促进Pol α。
Telomere integrity is maintained through end-protection proteins that block nuclease degradation and prevent telomeres from being recognized as DNA breaks. Although less well understood, end protection proteins may also play a role in facilitating telomere replication. Here, we show that overproduction (OP) of the yeast telomere capping protein Stn1 makes cells highly sensitive to the replication inhibitors hydroxyurea (HU) and methyl-methane sulfonate (MMS). Unexpectedly, this sensitivity corresponds with Stn1 OP blocking most, if not all, aspects of the S phase checkpoint. The checkpoint kinase Rad53 is phosphorylated with normal timing in Stn1 OP cells, indicating Stn1 does not interfere with signaling steps involved in activating the checkpoint. Part of the role of Stn1 in telomere integrity is mediated through the Pol12 subunit of DNA polymerase alpha (Pol alpha). We show that overproduced Stn1 generally associates with chromosomes in HU treated and untreated cells, and, remarkably, Stn1 chromosome binding and OP checkpoint defects are rescued in pol12 mutants. We propose Stn1 normally promotes Pol alpha activity at telomeres but can be recruited through Pol12 to nontelomeric sites when overproduced. During replication stress, the mislocalized Stn1 may inappropriately promote Pol alpha in a manner that interferes with Rad53 effector mechanisms controlling replication fork integrity.