Histone modifications play a critical role in the control over activities of the eukaryotic genome; among these chemical alterations, the methylation of lysine K9 in histone H3 (H3K9) is one of the most extensively studied. The number of enzymes capable of methylating H3K9 varies greatly across different organisms: in fission yeast, only one such methyltransferase is present, whereas in mammals, 10 are known. If there are several such enzymes, each of them must have some specific function, and they can interact with one another. Thus arises a complex system of interchangeability, “division of labor,” and contacts with each other and with diverse proteins. Histone methyltransferases specialize in the number of methyl groups that they attach and have different intracellular localizations as well as different distributions on chromosomes. Each also shows distinct binding to different types of sequences and has a specific set of nonhistone substrates.

中文翻译：

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H3K9 特异性组蛋白甲基转移酶的多样性和功能特化

组蛋白修饰在控制真核基因组活性中发挥着关键作用；在这些化学改变中，组蛋白 H3 (H3K9) 中赖氨酸 K9 的甲基化是研究最广泛的之一。不同生物体中能够甲基化 H3K9 的酶数量差异很大：在裂殖酵母中，仅存在一种这样的甲基转移酶，而在哺乳动物中，已知有 10 种。如果有多种这样的酶，则每种酶都必须具有某种特定的功能，并且它们可以相互作用。因此，出现了一个复杂的可互换性系统，“劳动分工”，以及彼此之间以及与不同蛋白质的接触。组蛋白甲基转移酶专门研究它们所附着的甲基基团的数量，并具有不同的细胞内定位以及染色体上的不同分布。每个还显示出与不同类型序列的不同结合，并具有一组特定的非组蛋白底物。