In eukaryotic nuclei, a number of phase‐separated nuclear bodies (NBs) are present. RNA polymerase II (Pol II) is the main player in transcription and forms large condensates in addition to localizing at numerous transcription foci. Cajal bodies (CBs) and histone locus bodies (HLBs) are NBs that are involved in transcriptional and post‐transcriptional regulation of small nuclear RNA and histone genes. By live‐cell imaging using human HCT116 cells, we here show that Pol II condensates (PCs) nucleated near CBs and HLBs, and the number of PCs increased during S phase concomitantly with the activation period of histone genes. Ternary PC–CB–HLB associates were formed via three pathways: nucleation of PCs and HLBs near CBs, interaction between preformed PC–HLBs with CBs and nucleation of PCs near preformed CB–HLBs. Coilin knockout increased the co‐localization rate between PCs and HLBs, whereas the number, nucleation timing and phosphorylation status of PCs remained unchanged. Depletion of PCs did not affect CBs and HLBs. Treatment with 1,6‐hexanediol revealed that PCs were more liquid‐like than CBs and HLBs. Thus, PCs are dynamic structures often nucleated following the activation of gene clusters associated with other NBs.

中文翻译：

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RNA聚合酶II冷凝物的形成，并与人活细胞中的Cajal和组蛋白基因座体缔合

在真核中，存在许多相分离的核体（NB）。RNA聚合酶II（Pol II）是转录的主要参与者，除了定位在许多转录位点外，还形成较大的缩合物。Cajal体（CBs）和组蛋白基因座体（HLBs）是NB，它们参与小核RNA和组蛋白基因的转录和转录后调控。通过使用人类HCT116细胞的活细胞成像，我们在这里显示Pol II凝结物（PC）在CB和HLB附近成核，并且PC数目在S期随组蛋白基因的激活期而增加。三元PC–CB–HLB缔合体通过三种途径形成：PC和HLB附近CB的成核，预制PC–HLB与CB之间的相互作用以及PC–HLB在预制CB–HLB附近的成核。盘绕敲除提高了PC和HLB之间的共定位率，而PC的数量，成核时间和磷酸化状态保持不变。PC的耗尽不会影响CB和HLB。用1,6-己二醇处理表明，与CB和HLB相比，PC更像液体。因此，PC是动态结构，通常在激活与其他NB相关的基因簇后成核。