UBF-binding site arrays form pseudo-NORs and sequester the RNA polymerase I transcription machinery
UBF-binding site arrays form pseudo-NORs and sequester the RNA polymerase I transcription machinery
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DOI：
10.1101/gad.310705
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发表时间：
2005-01-01
影响因子：
10.5
通讯作者：
McStay, B
中科院分区：
文献类型：
--
作者：
Mais, C;Wright, JE;McStay, B
人类核糖体基因（rDNA）位于近端着丝粒染色体短臂的核仁组成区（NOR）。在前一个细胞周期中转录活跃的中期NOR表现为显着的染色体特征，称为次级缢痕，其在染色体显带中为无色的，在银染色中为阳性。结构RNA聚合酶I（pol I）转录因子UBF在整个细胞周期中广泛地跨rDNA结合。为了确定UBF结合是否支持NOR结构，我们在人类染色体上的异位位点整合了大量异源UBF结合序列。这些阵列有效地招募UBF，甚至到核仁外的网站，并在中期，形成新的银纳米二次收缩，称为假NORs，形态学上类似的NORs。我们首次证明，除了UBF的其他组件的聚合酶I机器被发现与整个人类rDNA重复序列。值得注意的是，一个显着的分数，这些相同的聚合酶I因子被隔离的伪NORs独立的转录和核仁。由于采用的序列的异源性，我们推断，螯合主要是介导的蛋白质-蛋白质相互作用与UBF。这些结果表明，UBF的广泛结合是负责形成和维持的次级收缩在活跃的NORs。此外，我们建议，UBF介导招聘的聚合酶I机械核仁独立的启动子元件。
Human ribosomal genes (rDNA) are located in nucleolar organizer regions (NORs) on the short arms of acrocentric chromosomes. Metaphase NORs that were transcriptionally active in the previous cell cycle appear as prominent chromosomal features termed secondary constrictions that are achromatic in chromosome banding and positive in silver staining. The architectural RNA polymerase I (pol I) transcription factor UBF binds extensively across rDNA throughout the cell cycle. To determine if UBF binding underpins NOR structure, we integrated large arrays of heterologous UBF-binding sequences at ectopic sites on human chromosomes. These arrays efficiently recruit UBF even to sites outside the nucleolus and, during metaphase, form novel silver stainable secondary constrictions, termed pseudo-NORs, morphologically similar to NORs. We demonstrate for the first time that in addition to UBF the other components of the pol I machinery are found associated with sequences across the entire human rDNA repeat. Remarkably, a significant fraction of these same pol I factors are sequestered by pseudo-NORs independent of both transcription and nucleoli. Because of the heterologous nature of the sequence employed, we infer that sequestration is mediated primarily by protein-protein interactions with UBF. These results suggest that extensive binding of UBF is responsible for formation and maintenance of the secondary constriction at active NORs. Furthermore, we propose that UBF mediates recruitment of the pol I machinery to nucleoli independently of promoter elements.