Lehrstuhl Biochemie III, Universität Regensburg, Institut für Biochemie, Genetik und Mikrobiologie, 93053 Regensburg, Germany.
Cell. 2011 May 13;145(4):543-54. doi: 10.1016/j.cell.2011.03.051.
In eukaryotes, each of the more than 100 copies of ribosomal RNA (rRNA) genes exists in either an RNA polymerase I transcribed open chromatin state or a nucleosomal, closed chromatin state. Open rRNA genes guarantee the cell's supply with structural components of the ribosome, whereas closed rRNA genes ensure genomic integrity. We report that the observed balance between open and closed rRNA gene chromatin states in proliferating yeast cells is due to a dynamic equilibrium of transcription-dependent removal and replication-dependent assembly of nucleosomes. Pol I transcription is required for the association of the HMG box protein Hmo1 with open rRNA genes, counteracting replication-independent nucleosome deposition and maintaining the open rRNA gene chromatin state outside of S phase. The findings indicate that the opposing effects of replication and transcription lead to a de novo establishment of chromatin states for rRNA genes during each cell cycle.
在真核生物中，超过 100 个核糖体 RNA (rRNA) 基因的每一个都存在于 RNA 聚合酶 I 转录的开放染色质状态或核小体、封闭染色质状态中。开放的 rRNA 基因保证了细胞供应核糖体的结构成分，而封闭的 rRNA 基因则确保了基因组的完整性。我们报告说，在增殖酵母细胞中观察到的开放和封闭 rRNA 基因染色质状态之间的平衡是由于转录依赖性去除和复制依赖性组装核小体之间的动态平衡。Pol I 转录对于 HMG 盒蛋白 Hmo1 与开放 rRNA 基因的结合是必需的，这抵消了复制独立的核小体沉积，并在 S 期之外维持开放 rRNA 基因染色质状态。这些发现表明，复制和转录的相反作用导致 rRNA 基因在每个细胞周期中重新建立染色质状态。
