In eukaryotes, the genes encoding ribosomal RNAs (rDNA) exist in two distinct epigenetic states that can be distinguished by a specific chromatin structure that is maintained throughout the cell cycle and is inherited from one cell to another. The fact that even in proliferating cells with a high demand of protein synthesis a fraction of rDNA is silenced provides a unique possibility to decipher the mechanism underlying epigenetic regulation of rDNA. This chapter summarizes our knowledge of the molecular mechanisms that establish and propagate the epigenetic state of rRNA genes, unraveling a complex interplay of DNA methyltransferases and histone-modifying enzymes that act in concert with chromatin remodeling complexes and RNA-guided mechanisms to define the transcriptional state of rDNA. We also review the critical role of the RNA polymerase I transcription factor UBF in the formation of active nucleolar organizer regions (NORs) and maintenance of the euchromatic state of rRNA genes.

中文翻译：

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rRNA 基因的表观遗传学：从分子到染色体生物学。

在真核生物中，编码核糖体 RNA (rDNA) 的基因以两种不同的表观遗传状态存在，可以通过在整个细胞周期中保持并从一个细胞遗传到另一个细胞的特定染色质结构进行区分。即使在对蛋白质合成有高需求的增殖细胞中，一部分 rDNA 也被沉默，这一事实为破译 rDNA 表观遗传调控的潜在机制提供了独特的可能性。本章总结了我们对建立和传播 rRNA 基因表观遗传状态的分子机制的了解，揭示了 DNA 甲基转移酶和组蛋白修饰酶之间复杂的相互作用，这些酶与染色质重塑复合物和 RNA 引导机制协同作用以定义转录状态rDNA。