Cross S H, Meehan R R, Nan X, Bird A
Institute of Cell and Molecular Biology, Edinburgh University U.K.
Nat Genet. 1997 Jul;16(3):256-9. doi: 10.1038/ng0797-256.
Methylation of cytosines within the sequence CpG is essential for mouse development and has been linked to transcriptional suppression in vertebrate systems. Methyl-CpG binding proteins (MeCPs) 1 and 2 bind preferentially to methylated DNA and can inhibit transcription. The gene for MeCP2 has been cloned and a methyl-CpG binding domain (MBD) within it has been defined. A search of DNA sequence databases with the MBD sequence identified a human cDNA with potential to encode an MBD-like region. Sequencing of the complete cDNA revealed that the open reading frame also encodes two cysteine-rich domains that are found in animal DNA methyltransferases (DNMTs) and in the mammalian HRX protein (also known as MLL and All-1). HRX is related to Drosophila trithorax. The protein, known as Protein Containing MBD (PCM1), was expressed in bacteria and shown to bind specifically to methylated DNA. PCM1 also repressed transcription in vitro in a methylation-dependent manner. A polyclonal antibody raised against the protein was able to 'supershift' the native MeCP11 complex from HeLa cells, indicating that PCM1 is a component of mammalian MeCP1.
CpG序列中胞嘧啶的甲基化对小鼠发育至关重要，并且在脊椎动物系统中与转录抑制相关。甲基化CpG结合蛋白（MeCPs）1和2优先结合甲基化DNA，并能抑制转录。MeCP2基因已被克隆，其内部的一个甲基化CpG结合结构域（MBD）已被确定。用MBD序列搜索DNA序列数据库，鉴定出一个有潜力编码类似MBD区域的人类cDNA。对完整cDNA的测序表明，开放阅读框还编码两个富含半胱氨酸的结构域，这些结构域存在于动物DNA甲基转移酶（DNMTs）和哺乳动物HRX蛋白（也称为MLL和All-1）中。HRX与果蝇的三体胸苷相关。这种被称为含MBD蛋白（PCM1）的蛋白质在细菌中表达，并显示出能特异性结合甲基化DNA。PCM1在体外也以甲基化依赖的方式抑制转录。针对该蛋白产生的多克隆抗体能够使来自HeLa细胞的天然MeCP11复合物发生“超迁移移位”，表明PCM1是哺乳动物MeCP1的一个组成部分。
