Grummt Ingrid, Pikaard Craig S
Division of Molecular Biology of the Cell II, German Cancer Research Center, D-69120 Heidelberg, Germany.
Nat Rev Mol Cell Biol. 2003 Aug;4(8):641-9. doi: 10.1038/nrm1171.
The genes that encode ribosomal RNA exist in two distinct types of chromatin--an 'open' conformation that is permissive to transcription and a 'closed' conformation that is transcriptionally refractive. Recent studies have provided insights into the molecular mechanisms that silence either entire nucleolus organizer regions (NORs) in genetic hybrids or individual rRNA genes within a NOR. An emerging theme from these studies is that epigenetic mechanisms operating at the level of DNA methylation and histone modifications alter the chromatin structure and control the ratio of active and inactive rRNA genes.
编码核糖体RNA的基因存在于两种不同类型的染色质中——一种是允许转录的“开放”构象，另一种是转录惰性的“封闭”构象。最近的研究深入探讨了在遗传杂种中使整个核仁组织区（NORs）沉默或使NOR内单个rRNA基因沉默的分子机制。这些研究中一个新出现的主题是，在DNA甲基化和组蛋白修饰水平上起作用的表观遗传机制会改变染色质结构，并控制活性和非活性rRNA基因的比例。
