Jost J P, Hofsteenge J
Friedrich Miescher Institute, Basel, Switzerland.
Proc Natl Acad Sci U S A. 1992 Oct 15;89(20):9499-503. doi: 10.1073/pnas.89.20.9499.
MDBP-2 is a repressor that binds preferentially to methylated DNA. Peptides derived from MDBP-2 were sequenced. The sequences of the two peptides, KPAGPS-VTELITK and ALAAGGYDVEK, are identical to those found in the chicken histone H1 core protein. In SDS/polyacrylamide gels MDBP-2 has an apparent molecular mass of 21 kDa, and antibodies directed against calf thymus total histone H1 cross-react with MDBP-2. The preferential binding of affinity-purified MDBP-2 to methylated DNA is not sequence-specific but requires a minimum length of 30 base pairs and one pair of symmetrically methylated (i.e., methylated on both strands) CpG dinucleotides. As previously shown, there is a decrease in the binding activity of MDBP-2 to methylated DNA upon estradiol treatment. Immunoblots show that upon estradiol treatment the amount of immunocrossreacting MDBP-2 protein remains unchanged. MDBP-2 enables another protein to bind DNA which by itself does not bind methylated DNA. Ultraviolet crosslinking and selective immunoadsorption assays with anti-histone H1 antibodies show that in vivo MDBP-2 preferentially binds to the methylated repressed vitellogenin gene. It is concluded that MDBP-2 may participate in the long-term silencing of genes (formation of heterochromatin) through selective binding to methylated DNA.
MDBP - 2是一种优先与甲基化DNA结合的阻遏物。对源自MDBP - 2的肽段进行了测序。两种肽段KPAGPS - VTELITK和ALAAGGYDVEK的序列与鸡组蛋白H1核心蛋白中的序列相同。在SDS/聚丙烯酰胺凝胶中，MDBP - 2的表观分子量为21 kDa，针对小牛胸腺总组蛋白H1的抗体与MDBP - 2发生交叉反应。亲和纯化的MDBP - 2与甲基化DNA的优先结合并非序列特异性的，但需要至少30个碱基对的长度以及一对对称甲基化（即两条链上都甲基化）的CpG二核苷酸。如先前所示，雌二醇处理后MDBP - 2与甲基化DNA的结合活性降低。免疫印迹显示，雌二醇处理后免疫交叉反应性MDBP - 2蛋白的量保持不变。MDBP - 2能使另一种本身不与甲基化DNA结合的蛋白结合DNA。用抗组蛋白H1抗体进行的紫外线交联和选择性免疫吸附试验表明，在体内MDBP - 2优先与甲基化的受抑制卵黄生成素基因结合。得出的结论是，MDBP - 2可能通过与甲基化DNA的选择性结合参与基因的长期沉默（异染色质的形成）。
