Internal phase separation in synthetic DNA condensates

Biomolecular condensates regulate cellular biochemistry by organizing enzymes, substrates and metabolites, and often acquire partially de-mixed states whereby distinct internal domains play functional roles. Despite their physiological relevance, questions remain about the principles underpinning the emergece of multi-phase condensates. Here, we present a model system of synthetic DNA nanostructures able to form monophasic or biphasic condensates. Key condensate features, including the degree of interphase mixing and the relative size and spatial arrangement of domains, can be controlled by altering nanostructure stoichiometries. The modular nature of the system facilitates an intuitive understanding of phase behavior, and enables mapping of the experimental phenomenology onto a predictive Flory-Huggins model. The experimental and theoretical framework we introduce will help address open questions on multiphase condensation in biology and aid the design of functional biomolecular condensatesin vitro, in synthetic cells, and in living cells.