TERRA and hnRNPA1 orchestrate an RPA-to-POT1 switch on telomeric single-stranded DNA.
TERRA and hnRNPA1 orchestrate an RPA-to-POT1 switch on telomeric single-stranded DNA.
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DOI：
10.1038/nature09772
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发表时间：
2011-03-24
期刊：
影响因子：
64.8
通讯作者：
Zou, Lee
中科院分区：
文献类型：
--
作者：
Flynn, Rachel Litman;Centore, Richard C.;O'Sullivan, Roderick J.;Rai, Rekha;Tse, Alice;Zhou Songyang;Chang, Sandy;Karlseder, Jan;Zou, Lee
端粒的维持需要DNA复制和端粒的“加帽”的庇护。这两个过程使用两个单链DNA（ssDNA）结合蛋白，复制蛋白A（RPA）和端粒保护1（POT1）。虽然RPA和POT1在端粒中都有关键作用，但它们如何协同工作尚不清楚。POT1消融导致共济失调毛细血管扩张和Rad3相关（ATR）检查点激酶在端粒的激活，表明POT1拮抗RPA结合端粒ssDNA。出乎意料的是，我们发现纯化的POT1和它的功能伙伴TPP1不能有效地阻止RPA结合端粒ssDNA。在细胞提取物中，我们确定了一种新的活性，特异性地取代RPA，但不是POT1，从端粒ssDNA。使用纯化的蛋白质，我们表明，异质核核糖核蛋白A1（hnRNPA1）概括RPA置换活性。RPA置换活性在早期S期被含端粒重复序列的RNA（TERRA）抑制，但在晚期S期当TERRA水平在端粒处下降时释放。有趣的是，TERRA还通过去除hnRNPA1促进POT1与端粒ssDNA的结合，这表明TERRA在S期后的重新积累有助于完成端粒ssDNA上RPA到POT1的转换。总之，我们的数据表明，hnRNPA1，TERRA，和POT1的一致行动，以取代RPA从端粒的ssDNA后DNA复制，并促进端粒帽，以保持基因组的完整性。
Maintenance of telomeres requires both DNA replication and telomere ‘capping’ by shelterin. These two processes employ two single-stranded DNA (ssDNA)-binding proteins, replication protein A (RPA) and protection of telomeres 1 (POT1). Although RPA and POT1 each have a critical role at telomeres, how they function in concert is not clear. POT1 ablation leads to activation of the ataxia telangiectasia and Rad3-related (ATR) checkpoint kinase at telomeres, suggesting that POT1 antagonizes RPA binding to telomeric ssDNA. Unexpectedly, we found that purified POT1 and its functional partner TPP1 are unable to efficiently prevent RPA binding to telomeric ssDNA. In cell extracts, we identified a novel activity that specifically displaces RPA, but not POT1, from telomeric ssDNA. Using purified protein, we show that the heterogeneous nuclear ribonucleoprotein A1 (hnRNPA1) recapitulates the RPA displacing activity. The RPA displacing activity is inhibited by the telomeric repeat-containing RNA (TERRA) in early S phase, but is then unleashed in late S phase when TERRA levels decline at telomeres. Interestingly, TERRA also promotes POT1 binding to telomeric ssDNA by removing hnRNPA1, suggesting that the reaccumulation of TERRA after S phase helps to complete the RPA-to-POT1 switch on telomeric ssDNA. Together, our data suggest that hnRNPA1, TERRA, and POT1 act in concert to displace RPA from telomeric ssDNA following DNA replication, and promote telomere capping to preserve genomic integrity.
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