Nucleoli are multicomponent condensates defined by coexisting sub-phases. We identified distinct intrinsically disordered regions (IDRs), including acidic (D/E) tracts and K-blocks interspersed by E-rich regions, as defining features of nucleolar proteins. We show that the localization preferences of nucleolar proteins are determined by their IDRs and the types of RNA or DNA binding domains they encompass. In vitro reconstitutions and studies in cells showed how condensation, which combines binding and complex coacervation of nucleolar components, contributes to nucleolar organization. D/E tracts of nucleolar proteins contribute to lowering the pH of co-condensates formed with nucleolar RNAs in vitro. In cells, this sets up a pH gradient between nucleoli and the nucleoplasm. By contrast, juxta-nucleolar bodies, which have different macromolecular compositions, featuring protein IDRs with very different charge profiles, have pH values that are equivalent to or higher than the nucleoplasm. Our findings show that distinct compositional specificities generate distinct physicochemical properties for condensates.

核仁是由共存子相定义的多组分凝聚物。我们确定了不同的本质无序区域 (IDR)，包括酸性 (D/E) 区域和散布着富含 E 区域的 K 区，作为核仁蛋白的定义特征。我们表明，核仁蛋白的定位偏好是由它们的 IDR 以及它们所包含的 RNA 或 DNA 结合域的类型决定的。细胞的体外重建和研究表明，结合核仁成分的结合和复杂凝聚的凝聚如何有助于核仁组织。核仁蛋白的 D/E 束有助于降低体外与核仁 RNA 形成的共缩合物的 pH 值。在细胞中，这会在核仁和核质之间建立 pH 梯度。相比之下，近核仁体具有不同的大分子组成，其蛋白质IDR具有非常不同的电荷分布，其pH值等于或高于核质。我们的研究结果表明，不同的成分特异性会产生不同的冷凝物物理化学性质。