The repertoire of nucleobase methylation in DNA and RNA, introduced by chemical agents or enzymes, is large. Most methylation can be reversed either directly by restoration of the original nucleobase or indirectly by replacement of the methylated nucleobase with an unmodified nucleobase. In many direct and indirect demethylation reactions, ALKBH (AlkB homolog) and TET (ten eleven translocation) hydroxylases play a role. Here, we suggest a chemical classification of methylation types. We then discuss pathways for removal, emphasizing oxidation reactions. We highlight the recently expanded repertoire of ALKBH- and TET-catalyzed reactions and describe the discovery of a TET-like protein that resembles the hydroxylases but uses an alternative co-factor and catalyzes glyceryl transfer rather than hydroxylation.

由化学试剂或酶引入的DNA和RNA中核碱基甲基化的库很大。多数甲基化可通过原始核苷酸碱基的恢复直接逆转，或通过用未修饰的核苷酸碱基替代甲基化的核苷酸碱基而间接逆转。在许多直接和间接的脱甲基反应中，ALKBH（AlkB同源物）和TET（十一个11易位）羟化酶起作用。在这里，我们建议对甲基化类型进行化学分类。然后，我们讨论了去除途径，重点是氧化反应。我们着重介绍了最近扩展的ALKBH和TET催化反应的组成，并描述了类似于TET的蛋白的发现，该蛋白类似于羟化酶，但使用其他辅因子并催化甘油转移而不是羟化。