Biomolecular condensates are membrane-less organelles made of multiple components, often including several distinct proteins and nucleic acids. However, current tools to measure condensate composition are limited and cannot capture this complexity quantitatively, as they either require fluorescent labels, which we show can perturb composition, or can distinguish only 1-2 components. Here, we describe a label-free method based on quantitative phase microscopy to measure the composition of condensates with an arbitrarily large number of components. We first validate the method empirically in binary mixtures, revealing sequence-encoded density variation and complex aging dynamics for condensates composed of full-length proteins. In simplified multi-component protein/RNA condensates, we uncover a regime of constant condensate density and a large range of protein:RNA stoichiometry when varying average composition. The unexpected decoupling of density and composition highlights the need to determine molecular stoichiometry in multi-component condensates. We foresee this approach enabling the study of compositional regulation of condensate properties and function.

中文翻译：

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具有任意大量组分的生物分子缩合物的无标记成分测定

生物分子凝聚物是由多种成分组成的无膜细胞器，通常包括几种不同的蛋白质和核酸。然而，当前测量冷凝物成分的工具有限，无法定量捕获这种复杂性，因为它们要么需要荧光标记（我们证明荧光标记会扰乱成分），要么只能区分 1-2 种成分。在这里，我们描述了一种基于定量相显微镜的无标记方法，用于测量具有任意大量组分的冷凝物的组成。我们首先在二元混合物中凭经验验证该方法，揭示了由全长蛋白质组成的冷凝物的序列编码密度变化和复杂的老化动力学。在简化的多组分蛋白质/RNA 凝聚物中，当改变平均组成时，我们发现了恒定的冷凝物密度和大范围的蛋白质：RNA化学计量的体系。密度和组成的意外分离凸显了确定多组分缩合物中分子化学计量的必要性。我们预见这种方法能够研究冷凝物性质和功能的成分调节。