MBD2-MBD3 complex binds to hemi-methylated DNA and forms a complex containing DNMT1 at the replication foci in late S phase
MBD2-MBD3 complex binds to hemi-methylated DNA and forms a complex containing DNMT1 at the replication foci in late S phase
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DOI：
10.1046/j.1365-2443.2000.00359.x
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发表时间：
2000-08-01
期刊：
影响因子：
2.1
通讯作者：
Ishikawa, F
中科院分区：
文献类型：
--
作者：
Tatematsu, K;Yamazaki, T;Ishikawa, F
背景：在脊椎动物和植物中，DNA甲基化是调控基因表达的主要机制之一。最近已经鉴定了甲基-CpG结合蛋白家族，并且一些成员，如MeCP 2和MBD 2，显示通过将组蛋白脱乙酰酶复合物募集到甲基化基因来介导基因阻遏。结果：MBD 2和MBD 3在体内和体外均能形成同源和异源二聚体（或多聚体）。值得注意的是，MBD 2-MBD 3复合物显示出对半甲基化DNA的亲和力，这是家族蛋白质的任何成员从未报道过的性质。MBD 2和MBD 3与DNMT 1共定位于293细胞核中的复制灶，处于S期晚期。此外，通过免疫共沉淀实验，显示DNMT 1与MBD 2和MBD 3形成复合物。最后，MBD 3的丰度是最高的，在后期S期时，DNMT 1也是最丰富的，而MBD 2的水平在整个细胞cycles.Conclusions：结果表明，MBD 3可能在S期发挥重要作用。我们假设MBD 2-MBD 3复合物识别与DNA复制同时发生的半甲基化DNA，并招募组蛋白脱乙酰酶复合物以及DNMT 1，以建立和/或维持转录抑制的染色质。
Background: In vertebrates and plants, DNA methylation is one of the major mechanisms regulating gene expression. Recently a family of methyl-CpG-binding proteins has been identified, and some members, such as MeCP2 and MBD2, were shown to mediate gene repression by recruiting histone deacetylase complexes to methylated genes. However, the function of another member of this family, MBD3, remained elusive.Results: It was shown that MBD2 and MBD3 form homo- and hetero-dimers (or multimers) in vitro and in vivo. Significantly, the MBD2-MBD3 complex showed an affinity to hemi-methylated DNAs, a property that has never been reported with any member of the family proteins. MBD2 and MBD3 were co-localized with DNMT1 at replication foci in 293 cell nuclei at late S phase. Moreover, by a coimmunoprecipitation experiment, DNMT1 was shown to form a complex with MBD2 and MBD3. Finally, the abundance of MBD3 was highest in the late S phase when the DNMT1 is also most abundant, whereas the MBD2 level was largely constant throughout the cell cycle.Conclusions: The results suggest that MBD3 may play an important role in the S phase. We hypothesize that the MBD2-MBD3 complex recognizes hemimethylated DNA concurrent with DNA replication and recruits histone deacetylase complexes, as well as DNMT1, to establish and/or maintain the transcriptionally repressed chromatin.