Membrane-less organelles, known as biomolecular condensates, have emerged as dynamic hotspots for numerous cellular reactions. Liquid-liquid phase separation of molecules allows cells to compartmentalize biochemical reactions in these condensates without any physical barriers. Recent literature has provided plentiful examples of condensates that are driven by either kinetic or thermodynamic forces, in which proteins and nucleic acids are concentrated in different ratios. These condensates are often multilayered, with different compositions and material properties that change with time. Newly born protein-RNA condensates are typically homogeneous, but environmental perturbations, like temperature and slow diffusion of constituent molecules within the condensates, can lead to the creation of a dilute phase within the dense phase, thereby forming multilayer condensates. Such aging of condensates is accompanied by a gradual shift in the interactions between the molecules populating the condensates. It is believed that the conformational changes in the biomacromolecules lead to changes in the interactions among them.

In the study published in the January 7, 2025, issue of Biophysical Journal, Arosio and co-workers analyzed the aging of condensates composed of a helicase protein Dhh1 and a poly-U RNA model and provided an example of the formation of multicompartment condensates under kinetic control. The authors used fluorescence microscopy to investigate morphological changes in condensates over several days. As the condensates age, the poly-U RNA migrates from the dense to the dilute phase because of a decrease in the relative strength of the protein-RNA interaction in the condensate. The effect of the size of the condensate was also studied on the formation of double-emulsion condensates over time, and a critical condensate size was established. For a larger poly-U RNA, there is a more significant number of protein-RNA interactions per poly-U molecule, and the tendency to migrate toward the dilute phase was found to decrease.

The study has significant implications in biology because biomolecular condensate aging has been linked to numerous pathological states. The study also has implications for material sciences for developing kinetically controlled double-emulsion condensates.