Li Qi, Wang Xiaokang, Sun Han, Zeng Jun, Cao Zhendong, Li Yan, Qian Weiqiang
State Key Laboratory of Protein and Plant Gene Research, The Peking-Tsinghua Center for Life Sciences, School of Advanced Agricultural Sciences and School of Life Sciences, Peking University, Beijing, China.
PLoS Genet. 2015 May 1;11(5):e1005210. doi: 10.1371/journal.pgen.1005210. eCollection 2015 May.
Active DNA demethylation plays crucial roles in the regulation of gene expression in both plants and animals. In Arabidopsis thaliana, active DNA demethylation is initiated by the ROS1 subfamily of 5-methylcytosine-specific DNA glycosylases via a base excision repair mechanism. Recently, IDM1 and IDM2 were shown to be required for the recruitment of ROS1 to some of its target loci. However, the mechanism(s) by which IDM1 is targeted to specific genomic loci remains to be determined. Affinity purification of IDM1- and IDM2- associating proteins demonstrated that IDM1 and IDM2 copurify together with two novel components, methyl-CpG-binding domain protein 7 (MBD7) and IDM2-like protein 1 (IDL1). IDL1 encodes an α-crystallin domain protein that shows high sequence similarity with IDM2. MBD7 interacts with IDM2 and IDL1 in vitro and in vivo and they form a protein complex associating with IDM1 in vivo. MBD7 directly binds to the target loci and is required for the H3K18 and H3K23 acetylation in planta. MBD7 dysfunction causes DNA hypermethylation and silencing of reporter genes and a subset of endogenous genes. Our results suggest that a histone acetyltransferase complex functions in active DNA demethylation and in suppression of gene silencing at some loci in Arabidopsis.
主动DNA去甲基化在植物和动物的基因表达调控中都起着关键作用。在拟南芥中，主动DNA去甲基化由5-甲基胞嘧啶特异性DNA糖基化酶的ROS1亚家族通过碱基切除修复机制启动。最近研究表明，IDM1和IDM2是ROS1募集到其某些靶位点所必需的。然而，IDM1靶向特定基因组位点的机制仍有待确定。对与IDM1和IDM2相关蛋白的亲和纯化表明，IDM1和IDM2与两个新组分，即甲基-CpG结合域蛋白7（MBD7）和IDM2样蛋白1（IDL1）一起共纯化。IDL1编码一种与IDM2具有高度序列相似性的α-晶状体蛋白结构域蛋白。MBD7在体外和体内均与IDM2和IDL1相互作用，并且它们在体内形成与IDM1相关的蛋白质复合物。MBD7直接结合到靶位点，并且是植物中H3K18和H3K23乙酰化所必需的。MBD7功能障碍导致报告基因和一部分内源基因的DNA超甲基化和沉默。我们的结果表明，组蛋白乙酰转移酶复合物在拟南芥的某些位点的主动DNA去甲基化和基因沉默抑制中起作用。
