Department of Laboratory Medicine and Pathology, Yale University School of Medicine, New Haven, CT 06520, USA.
Cell Res. 2013 May;23(5):705-19. doi: 10.1038/cr.2013.31. Epub 2013 Mar 5.
Human single-strand (ss) DNA binding proteins 1 and 2 (hSSB1 and 2) are components of the hSSB1/2-INTS3-C9orf80 heterotrimeric protein complex shown to participate in DNA damage response and maintenance of genome stability. However, their roles at telomeres remain unknown. Here, we generated murine SSB1 conditional knockout mice and cells and found that mSSB1 plays a critical role in telomere end protection. Both mSSB1 and mSSB2 localize to a subset of telomeres and are required to repair TRF2-deficient telomeres. Deletion of mSSB1 resulted in increased chromatid-type fusions involving both leading- and lagging-strand telomeric DNA, suggesting that it is required for the protection of G-overhangs. mSSB1's interaction with INTS3 is required for its localization to damaged DNA. mSSB1 interacts with Pot1a, but not Pot1b, and its association with telomeric ssDNA requires Pot1a. mSSB1(Δ/Δ) mice die at birth with developmental abnormalities, while mice with the hypomorphic mSSB1(F/F) allele are born alive and display increased sensitivity to ionizing radiation (IR). Our results suggest that mSSB1 is required to maintain genome stability, and document a previously unrecognized role for mSSB1/2 in the protection of newly replicated leading- and lagging-strand telomeres.
人单链（ss）DNA 结合蛋白 1 和 2（hSSB1 和 2）是 hSSB1/2-INTS3-C9orf80 异三聚体蛋白复合物的组成部分，该复合物被证明参与 DNA 损伤反应和基因组稳定性的维持。然而，它们在端粒上的作用仍然未知。在这里，我们生成了小鼠 SSB1 条件性敲除小鼠和细胞，并发现 mSSB1 在端粒末端保护中起着关键作用。mSSB1 和 mSSB2 都定位于一部分端粒上，并且需要修复 TRF2 缺陷型端粒。mSSB1 的缺失导致涉及前导链和滞后链端粒 DNA 的染色单体型融合增加，表明它需要保护 G 突出端。mSSB1 与 INTS3 的相互作用是其定位到受损 DNA 所必需的。mSSB1 与 Pot1a 相互作用，但不与 Pot1b 相互作用，并且它与端粒 ssDNA 的结合需要 Pot1a。mSSB1(Δ/Δ) 小鼠在出生时因发育异常而死亡，而具有低功能 mSSB1(F/F) 等位基因的小鼠出生时存活，并对电离辐射（IR）表现出更高的敏感性。我们的结果表明，mSSB1 是维持基因组稳定性所必需的，并记录了 mSSB1/2 在保护新复制的前导链和滞后链端粒方面的以前未被认识到的作用。
