Kautiainen T L, Jones P A
Biochemistry. 1985 Feb 26;24(5):1193-6. doi: 10.1021/bi00326a021.
The inheritance of DNA methylation patterns may play an important role in the stability of the differentiated state. We have therefore studied the inhibitory effects of DNA binding proteins on DNA methylation in vitro. Mouse L1210 cells grown in the presence of 5-azacytidine acquire hemimethylated sites in their DNA. Purified hemimethylated DNA accepted methyl groups from S-adenosyl-L-methionine in the presence of a crude maintenance methylase more readily than purified DNA isolated from cells not exposed to 5-azacytidine. On the other hand, chromatin fractions isolated from cells grown in the presence or absence of 5-azacytidine were poor substrates for the maintenance methylase irrespective of the number of hemimethylated sites present in the DNA. Inhibition of DNA methylation was shown to be associated primarily with chromatin proteins bound to DNA, and trypsinization of nuclei increased their methyl accepting abilities. Methyl acceptance was increased by salt extraction of chromosomal proteins. These data suggest that association of histones with DNA may play a role in the modulation of methylation patterns.
DNA甲基化模式的遗传可能在分化状态的稳定性中起重要作用。因此，我们研究了DNA结合蛋白在体外对DNA甲基化的抑制作用。在5-氮杂胞苷存在下生长的小鼠L1210细胞在其DNA中获得半甲基化位点。与从未接触过5-氮杂胞苷的细胞中分离的纯化DNA相比，纯化的半甲基化DNA在粗制维持甲基转移酶存在的情况下更易从S-腺苷-L-甲硫氨酸接受甲基基团。另一方面，无论DNA中存在的半甲基化位点数量如何，从在有或没有5-氮杂胞苷的情况下生长的细胞中分离的染色质组分都是维持甲基转移酶的不良底物。DNA甲基化的抑制主要与结合到DNA上的染色质蛋白有关，细胞核的胰蛋白酶处理增加了它们的甲基接受能力。通过盐提取染色体蛋白可增加甲基接受能力。这些数据表明组蛋白与DNA的结合可能在甲基化模式的调节中起作用。
