Downs J A, Lowndes N F, Jackson S P
The Wellcome Trust and Cancer Research Campaign, Institute of Cancer and Developmental Biology, and Department of Zoology, University of Cambridge, UK.
Nature. 2000;408(6815):1001-4. doi: 10.1038/35050000.
Histone proteins associate with and compact eukaryotic nuclear DNA to form chromatin. The basic unit of chromatin is the nucleosome, which is made up of 146 base pairs of DNA wrapped around two of each of four core histones, H2A, H2B, H3 and H4. Chromatin structure and its regulation are important in transcription and DNA replication. We therefore thought that DNA-damage signalling and repair components might also modulate chromatin structure. Here we have characterized a conserved motif in the carboxy terminus of the core histone H2A from Saccharomyces cerevisiae that contains a consensus phosphorylation site for phosphatidylinositol-3-OH kinase related kinases (PIKKs). This motif is important for survival in the presence of agents that generate DNA double-strand breaks, and the phosphorylation of this motif in response to DNA damage is dependent on the PIKK family member Mec1. The motif is not necessary for Mec1-dependent cell-cycle or transcriptional responses to DNA damage, but is required for efficient DNA double-strand break repair by non-homologous end joining. In addition, the motif has a role in determining higher order chromatin structure. Thus, phosphorylation of a core histone in response to DNA damage may cause an alteration of chromatin structure that facilitates DNA repair.
组蛋白与真核细胞核DNA结合并使其压缩，从而形成染色质。染色质的基本单位是核小体，它由146个碱基对的DNA缠绕在四种核心组蛋白（H2A、H2B、H3和H4）各两个分子上组成。染色质结构及其调控在转录和DNA复制过程中起着重要作用。因此，我们认为DNA损伤信号传导和修复组件可能也会调节染色质结构。在此，我们鉴定了酿酒酵母核心组蛋白H2A羧基末端的一个保守基序，该基序包含磷脂酰肌醇-3-羟基激酶相关激酶（PIKKs）的共有磷酸化位点。这个基序对于在产生DNA双链断裂的试剂存在下的细胞存活很重要，并且该基序在响应DNA损伤时的磷酸化依赖于PIKK家族成员Mec1。该基序对于Mec1依赖的细胞周期或对DNA损伤的转录反应不是必需，但对于通过非同源末端连接进行有效的DNA双链断裂修复是必需的。此外，该基序在决定高阶染色质结构方面发挥作用。因此，响应DNA损伤的核心组蛋白磷酸化可能会导致染色质结构改变，从而促进DNA修复。
