Ribes-Zamora Albert, Mihalek Ivana, Lichtarge Olivier, Bertuch Alison A
Department of Pediatrics, Hematology/Oncology Section, Baylor College of Medicine, One Baylor Plaza, BCM225, Houston, Texas 77030-3411, USA.
Nat Struct Mol Biol. 2007 Apr;14(4):301-7. doi: 10.1038/nsmb1214. Epub 2007 Mar 11.
The Ku heterodimer, comprised of Ku70 and Ku80 subunits, is a conserved complex involved in nonhomologous end-joining (NHEJ). However, it also functions in maintenance of telomeres, chromosome termini normally resistant to end-joining events. To elucidate the spatial organization of these functions, we rationally guided Ku mutagenesis in yeast with real-valued evolutionary trace (rvET). This revealed two ancestrally related alpha-helices: one on the Ku70 surface that is required in yeast for NHEJ, and a second on the Ku80 surface that is required in yeast for telomeric heterochromatin formation. When bound to a DNA end, the surface containing the NHEJ-specific Ku70 helix is oriented toward the DNA terminus, whereas the surface containing the telomeric function-specific Ku80 helix faces inward, toward telomeric chromatin, when bound to a telomere. We propose a 'two-face' model for Ku and that divergent evolution of these faces allowed Ku's dual role in NHEJ and telomere maintenance.
由Ku70和Ku80亚基组成的Ku异源二聚体是一种参与非同源末端连接（NHEJ）的保守复合物。然而，它也在端粒的维持中发挥作用，端粒是通常对末端连接事件具有抗性的染色体末端。为了阐明这些功能的空间组织，我们利用实值进化追踪（rvET）在酵母中合理地指导Ku诱变。这揭示了两个祖先相关的α螺旋：一个在Ku70表面，是酵母中NHEJ所必需的；另一个在Ku80表面，是酵母中形成端粒异染色质所必需的。当与DNA末端结合时，含有NHEJ特异性Ku70螺旋的表面朝向DNA末端，而当与端粒结合时，含有端粒功能特异性Ku80螺旋的表面朝内，朝向端粒染色质。我们提出了一个关于Ku的“双面”模型，并且这些面的趋异进化使得Ku在NHEJ和端粒维持中具有双重作用。
