The nucleolus as a polarized coaxial cable in which the rDNA axis is surrounded by dynamic subunit-specific phases.
The nucleolus as a polarized coaxial cable in which the rDNA axis is surrounded by dynamic subunit-specific phases.
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DOI：
10.1016/j.cub.2021.03.041
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发表时间：
2021-06-21
期刊：
影响因子：
--
通讯作者：
Woolford JL Jr
中科院分区：
文献类型：
--
作者：
Tartakoff AM;Chen L;Raghavachari S;Gitiforooz D;Dhinakaran A;Ni CL;Pasadyn C;Mahabeleshwar GH;Pasadyn V;Woolford JL Jr
在核糖体DNA（rDNA）重复序列中，编码小亚基（SSU）rRNA的序列先于编码大亚基（LSU）rRNA的序列。处理复合转录物和亚基组装需要>100个亚基特异性核仁组装因子（AF）。为了研究核仁的功能组织，我们定位了S。酿酒酵母，其中rDNA轴被“线性化”以降低其维度，从而揭示其同轴组织。在这种情况下，rRNA合成和加工继续进行。轴嵌入在由LSU AF的外层/相围绕的SSU AF的内层/相中。当亚基产生被抑制时，AF的子集在内层和外层之间差异性地重新定位，正如预期的那样，如果存在重复重新定位的循环，则“潜伏”AF在被招募到新生亚基时变得“有效”。识别AF循环和rRNA片段的定位使得可以推断跨越内层和外层之间的组装中间体的存在，并绘制每个亚基的共转录组装。AF循环也可以解释在核仁中具有多于一个蛋白质相如何使得“矢量2相分配”成为新生rRNP重新定位的驱动力。由于核质AF也存在于外层，我们建议，关键的表面重塑发生在这个网站上，从而分区亚基前体到核质的转录后成熟。与高等真核生物的观察结果相比，同轴范式可能适用于许多其他具有rDNA重复序列的生物。Tartakoff等人记录了酵母核仁的同轴组织，其中rDNA轴被亚基组装因子的两个动态层/阶段包围，所述亚基组装因子在每个转录周期期间在潜伏状态和操作状态之间交替。
In ribosomal DNA (rDNA) repeats, sequences encoding small subunit (SSU) rRNA precede those encoding large subunit (LSU) rRNAs. Processing the composite transcript and subunit assembly requires >100 subunit-specific nucleolar assembly factors (AFs). To investigate the functional organization of the nucleolus, we localized AFs in S. cerevisiae in which the rDNA axis was “linearized” to reduce its dimensionality, thereby revealing its coaxial organization. In this situation rRNA synthesis and processing continue. The axis is embedded in an inner layer/phase of SSU AFs that is surrounded by an outer layer/phase of LSU AFs. When subunit production is inhibited, subsets of AFs differentially relocate between the inner and outer layers, as expected if there is a cycle of repeated relocation whereby “latent” AFs become “operative” when recruited to nascent subunits. Recognition of AF cycling and localization of segments of rRNA make it possible to infer the existence of assembly intermediates that span between the inner and outer layers, and to chart the cotranscriptional assembly of each subunit. AF cycling also can explain how having more than one protein phase in the nucleolus makes possible “vectorial 2-phase partitioning” as a driving force for relocation of nascent rRNPs. Since nucleoplasmic AFs are also present in the outer layer, we propose that critical surface remodeling occurs at this site, thereby partitioning subunit precursors into the nucleoplasm for post-transcriptional maturation. Comparison to observations on higher eukaryotes shows that the coaxial paradigm is likely to be applicable for the many other organisms that have rDNA repeats. Tartakoff et al. document the coaxial organization of the yeast nucleolus in which the rDNA axis is surrounded by two dynamic layers/phases of subunit assembly factors that alternate between latent and operative states during each transcription cycle.
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影响因子：
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