The de novo methylation activity of Dnmt3a is distinctly different than that of Dnmt1.
The de novo methylation activity of Dnmt3a is distinctly different than that of Dnmt1.
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DOI：
10.1186/1471-2091-6-6
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发表时间：
2005-03-30
期刊：
影响因子：
--
通讯作者：
Hsieh CL
中科院分区：
文献类型：
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作者：
Hsieh CL
虽然Dnmt1被认为是哺乳动物中主要的维持甲基转移酶，DNMT3a和Dnmt3b被认为是从头开始的甲基转移酶，但这三种酶可能共同维持和建立DNA甲基化模式。有人提出，Dnmt1可以在基因组中具有瞬时单链区域的位置进行从头甲基化，例如复制起点，然后在体内从这些核化位置传播甲基化，尽管这种活性尚未报道。在这项研究中，我们发现DNMT3A在体外不作用于单链底物，这表明DNMT3A不太可能在这些建议的成核位置启动DNA甲基化。DNMT3A在未甲基化和半甲基化的双链DNA上表现出相似的甲基化活性，但有一些底物偏好。与DNMT1不同的是，在体外和体内，CpG或非CpG位点上预先存在的胞嘧啶甲基化不会刺激DNMT3A的活性。DNMT3A不作用于单链DNA，也不受预先存在的胞嘧啶甲基化的刺激，这表明DNMT3A的从头甲基化活性与Dnmt1有很大的不同。这些发现与DNMT3A在双链DNA的一条DNA链上启动甲基化，然后这些半甲基化位点刺激DNMT1活性进行进一步甲基化的模型是一致的。
Though Dnmt1 is considered the primary maintenance methyltransferase and Dnmt3a and Dnmt3b are considered de novo methyltransferases in mammals, these three enzymes may work together in maintaining as well as establishing DNA methylation patterns. It has been proposed that Dnmt1 may carry out de novo methylation at sites in the genome with transient single-stranded regions, such as replication origins, and then spread methylation from these nucleation sites in vivo, even though such activity has not been reported. In this study, we show that Dnmt3a does not act on single-stranded substrates in vitro, indicating that Dnmt3a is not likely to initiate DNA methylation at such proposed nucleation sites. Dnmt3a shows similar methylation activity on unmethylated and hemimethylated duplex DNA, though with some substrate preference. Unlike Dnmt1, pre-existing cytosine methylation at CpG sites or non-CpG sites does not stimulate Dnmt3a activity in vitro and in vivo. The fact that Dnmt3a does not act on single stranded DNA and is not stimulated by pre-existing cytosine methylation indicates that the de novo methylation activity of Dnmt3a is quite different from that of Dnmt1. These findings are consistent with a model in which Dnmt3a initiates methylation on one of the DNA strands of duplex DNA, and these hemimethylated sites then stimulate Dnmt1 activity for further methylation.