Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA.
Nat Struct Mol Biol. 2011 Apr;18(4):478-85. doi: 10.1038/nsmb.2033. Epub 2011 Mar 13.
Telomere capping conceals chromosome ends from exonucleases and checkpoints, but the full range of capping mechanisms is not well defined. Telomeres have the potential to form G-quadruplex (G4) DNA, although evidence for telomere G4 DNA function in vivo is limited. In budding yeast, capping requires the Cdc13 protein and is lost at nonpermissive temperatures in cdc13-1 mutants. Here, we use several independent G4 DNA-stabilizing treatments to suppress cdc13-1 capping defects. These include overexpression of three different G4 DNA binding proteins, loss of the G4 DNA unwinding helicase Sgs1, or treatment with small molecule G4 DNA ligands. In vitro, we show that protein-bound G4 DNA at a 3' overhang inhibits 5'→3' resection of a paired strand by exonuclease I. These findings demonstrate that, at least in the absence of full natural capping, G4 DNA can play a positive role at telomeres in vivo.
端粒加帽将染色体末端与外切核酸酶和检验点隔离开来，但端粒加帽的机制还没有被完全定义。端粒有形成 G-四链体（G4 DNA）的潜力，尽管体内端粒 G4 DNA 功能的证据有限。在 budding yeast 中，加帽需要 Cdc13 蛋白，并且在 cdc13-1 突变体中在非许可温度下丢失。在这里，我们使用几种独立的 G4 DNA 稳定处理方法来抑制 cdc13-1 的加帽缺陷。这些方法包括过表达三种不同的 G4 DNA 结合蛋白、丧失 G4 DNA 解旋酶 Sgs1 或用小分子 G4 DNA 配体处理。在体外，我们表明 3'突出端的蛋白结合 G4 DNA 抑制外切核酸酶 I 对配对链的 5'→3'切除。这些发现表明，至少在没有完全自然加帽的情况下，G4 DNA 可以在体内的端粒中发挥积极作用。
