Javaheri Ali, Wysocki Robert, Jobin-Robitaille Olivier, Altaf Mohammed, Côté Jacques, Kron Stephen J
Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
Proc Natl Acad Sci U S A. 2006 Sep 12;103(37):13771-6. doi: 10.1073/pnas.0511192103. Epub 2006 Aug 29.
Recent studies of yeast G1 DNA damage response have identified characteristic changes in chromatin adjacent to double-strand breaks (DSBs). Histone H2A (yeast H2AX) is rapidly phosphorylated on S129 by the kinase Tel1 (ATM) over a domain extending kilobases from the DSB. The adaptor protein Rad9 (53BP1) is recruited to this chromatin domain through binding of its tudor domains to histone H3 diMe-K79. Multisite phosphorylation of Rad9 by Mec1 (ATR) then activates the signaling kinase Rad53 (CHK2) to induce a delay in G1. Here, we report a previously undescribed role for Tel1 in G1 checkpoint response and show that H2A is the likely phosphorylation target, in a much as S129 mutation to Ala confers defects in G1 checkpoint arrest, Rad9 phosphorylation, and Rad53 activation. Importantly, Rad9 fails to bind chromatin adjacent to DSBs in H2A-S129A mutants. Previous work showed that H2A phosphorylation allows binding of NuA4, SWR, and INO80 chromatin remodeling complexes, perhaps exposing H3 diMe-K79. Yet, mutants lacking SWR or INO80 remain checkpoint competent, whereas loss of NuA4-dependent histone acetylation leads to G1 checkpoint persistence, suggesting that H2A phosphorylation promotes two independent events, rapid Rad9 recruitment to DSBs and subsequent remodeling by NuA4, SWR, and INO80.
最近对酵母G1期DNA损伤反应的研究已经确定了双链断裂（DSB）附近染色质的特征性变化。组蛋白H2A（酵母中的H2AX）在激酶Tel1（ATM）的作用下，在S129位点迅速磷酸化，磷酸化区域从DSB延伸数千碱基。衔接蛋白Rad9（53BP1）通过其tudor结构域与组蛋白H3二甲基化的K79结合，被招募到这个染色质区域。然后，Mec1（ATR）对Rad9进行多位点磷酸化，激活信号激酶Rad53（CHK2），从而在G1期诱导延迟。在这里，我们报道了Tel1在G1期检查点反应中一个以前未被描述的作用，并表明H2A可能是磷酸化靶点，因为将S129突变为丙氨酸会导致G1期检查点停滞、Rad9磷酸化和Rad53激活出现缺陷。重要的是，在H2A - S129A突变体中，Rad9无法与DSB附近的染色质结合。先前的研究表明，H2A磷酸化允许NuA4、SWR和INO80染色质重塑复合物结合，这可能会暴露H3二甲基化的K79。然而，缺乏SWR或INO80的突变体仍具有检查点功能，而NuA4依赖的组蛋白乙酰化缺失会导致G1期检查点持续存在，这表明H2A磷酸化促进了两个独立的事件，即Rad9迅速招募到DSB以及随后由NuA4、SWR和INO80进行的重塑。
