Gaston K, Fried M
Department of Biochemistry, School of Medical Sciences, University of Bristol, UK.
Nucleic Acids Res. 1995 Mar 25;23(6):901-9. doi: 10.1093/nar/23.6.901.
The divergently transcribed Surf-1 and Surf-2 housekeeping genes are separated by a bi-directional, TATA-less promoter which lies within a CpG-rich island. Here we show that CpG methylation severely reduces transcription in the direction of both Surf-1 and Surf-2. Previous work has identified three promoter elements (Su1, Su2 and Su3) which are conserved between the human and mouse Surf-1/Surf-2 promoters. These elements bind transcription factors present in human and mouse cell nuclear extracts in vitro and mutations which prevent factor binding also reduce promoter activity in vivo. Transcription initiation factor YY1 binds to the Su1 site and stimulates transcription in the direction of Surf-1 and, to a lesser extent, Surf-2. Here we show that members of the ETS family of transcription factors bind to the Su2 site. Although the Su1 factor binding site contains three CpG dinucleotides, the binding of YY1 is not affected by CpG methylation. In contrast, CpG methylation abolishes the binding of ETS proteins to the Su2 site; methylation of a single cytosine, at position 3 of the consensus ETS site, is sufficient to prevent factor binding. This direct effect on the binding of ETS proteins is, however, not in itself sufficient to explain the repression of this promoter by CpG methylation. A mutation of the Su2 site which removes the sequence CpG, but which does not prevent ETS factor binding, fails to relieve this promoter from repression by CpG methylation.
反向转录的看家基因Surf-1和Surf-2被一个位于富含CpG岛中的双向、无TATA框启动子分隔开。我们在此表明，CpG甲基化严重降低了Surf-1和Surf-2方向上的转录。先前的研究已经确定了三个人类和小鼠Surf-1/Surf-2启动子之间保守的启动子元件（Su1、Su2和Su3）。这些元件在体外与人及小鼠细胞核提取物中存在的转录因子结合，而阻止因子结合的突变也会降低体内启动子活性。转录起始因子YY1与Su1位点结合，并在Surf-1方向上刺激转录，在较小程度上也刺激Surf-2方向上的转录。我们在此表明，ETS转录因子家族成员与Su2位点结合。尽管Su1因子结合位点包含三个CpG二核苷酸，但YY1的结合不受CpG甲基化影响。相反，CpG甲基化消除了ETS蛋白与Su2位点的结合；在ETS共有位点第3位的单个胞嘧啶甲基化就足以阻止因子结合。然而，这种对ETS蛋白结合的直接影响本身不足以解释该启动子因CpG甲基化而受到的抑制。去除序列CpG但不阻止ETS因子结合的Su2位点突变，无法使该启动子免受CpG甲基化的抑制。
