Teo S H, Jackson S P
Wellcome Trust and Cancer Research Campaign, Institute of Cancer and Developmental Biology, University of Cambridge, Cambridge CB2 1QR, UK.
EMBO Rep. 2001 Mar;2(3):197-202. doi: 10.1093/embo-reports/kve038.
Ku is a conserved heterodimeric DNA-binding protein that plays critical roles in DNA repair and telomere homeostasis. In Saccharomyces cerevisiae, deletion of YKU70 or YKU80 results in an inability to grow at 37 degrees C. This is suppressed by overexpression of several components of telomerase (EST1, EST2 and TLC1). We show that overexpression of EST2 or TLC1 in yku80 mutants does not restore efficient DNA repair, or restore normal telomere function, as measured by telomere length, single-stranded G-rich strand or transcriptional silencing. Instead, yku80 mutants activate a Rad53p-dependent DNA-damage checkpoint at 37 degrees C and this is suppressed by overexpression of EST2 or TLC1. Indeed, deletion of genes required for Rad53p activation also suppresses the yku80 temperature sensitivity. These results suggest that activation of the DNA-damage checkpoint in yku mutants at 37 degrees C does not result from reduced telomere length per se, but reflects an alteration of the telomere structure that is recognized as damaged DNA.
Ku是一种保守的异源二聚体DNA结合蛋白，在DNA修复和端粒稳态中发挥关键作用。在酿酒酵母中，缺失YKU70或YKU80会导致无法在37℃下生长。这可通过端粒酶的几个组分（EST1、EST2和TLC1）的过表达得到抑制。我们发现，在yku80突变体中过表达EST2或TLC1并不能恢复有效的DNA修复，也不能恢复正常的端粒功能，这是通过端粒长度、富含鸟嘌呤的单链或转录沉默来衡量的。相反，yku80突变体在37℃时激活了依赖Rad53p的DNA损伤检查点，而EST2或TLC1的过表达可抑制这一现象。实际上，缺失Rad53p激活所需的基因也可抑制yku80的温度敏感性。这些结果表明，yku突变体在37℃时DNA损伤检查点的激活并非源于端粒长度本身的缩短，而是反映了端粒结构的改变，这种改变被识别为受损DNA。
