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rDNA 是由聚合物-聚合物相分离形成的生物分子凝聚物,并通过转录和 R 环被隔离在核仁中。

The rDNA is biomolecular condensate formed by polymer-polymer phase separation and is sequestered in the nucleolus by transcription and R-loops.

机构信息

Biology Department, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.

出版信息

Nucleic Acids Res. 2021 May 7;49(8):4586-4598. doi: 10.1093/nar/gkab229.

Abstract

The nucleolus is the site of ribosome biosynthesis encompassing the ribosomal DNA (rDNA) locus in a phase separated state within the nucleus. In budding yeast, we find the rDNA locus and Cdc14, a protein phosphatase that co-localizes with the rDNA, behave like a condensate formed by polymer-polymer phase separation, while ribonucleoproteins behave like a condensate formed by liquid-liquid phase separation. The compaction of the rDNA and Cdc14's nucleolar distribution are dependent on the concentration of DNA cross-linkers. In contrast, ribonucleoprotein nucleolar distribution is independent of the concentration of DNA cross-linkers and resembles droplets in vivo upon replacement of the endogenous rDNA locus with high-copy plasmids. When ribosomal RNA is transcribed from the plasmids by Pol II, the rDNA-binding proteins and ribonucleoprotein signals are weakly correlated, but upon repression of transcription, ribonucleoproteins form a single, stable droplet that excludes rDNA-binding proteins from its center. Degradation of RNA-DNA hybrid structures, known as R-loops, by overexpression of RNase H1 results in the physical exclusion of the rDNA locus from the nucleolar center. Thus, the rDNA locus is a polymer-polymer phase separated condensate that relies on transcription and physical contact with RNA transcripts to remain encapsulated within the nucleolus.

摘要

核仁是核糖体生物合成的场所,包含核内相分离状态下的核糖体 DNA(rDNA)基因座。在 budding yeast 中,我们发现 rDNA 基因座和 Cdc14(一种与 rDNA 共定位的蛋白磷酸酶)的行为类似于聚合物-聚合物相分离形成的凝聚物,而核糖核蛋白则类似于液体-液体相分离形成的凝聚物。rDNA 和 Cdc14 的核仁分布的压缩依赖于 DNA 交联剂的浓度。相比之下,核糖核蛋白的核仁分布与 DNA 交联剂的浓度无关,并且在用高拷贝质粒替换内源性 rDNA 基因座后,在体内类似于液滴。当 Pol II 从质粒转录核糖体 RNA 时,rDNA 结合蛋白和核糖核蛋白信号之间的相关性较弱,但在转录被抑制后,核糖核蛋白形成一个单一、稳定的液滴,将 rDNA 结合蛋白排除在其中心之外。通过过度表达 RNase H1 降解 RNA-DNA 杂交结构(称为 R 环)会导致 rDNA 基因座从核仁中心的物理排斥。因此,rDNA 基因座是一种聚合物-聚合物相分离的凝聚物,它依赖于转录和与 RNA 转录本的物理接触来保持封装在核仁内。

https://cdn.ncbi.nlm.nih.gov/pmc/blobs/8dd8/8096216/8e0e96e10939/gkab229fig1.jpg

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