eLife assessment
The authors report results from experiments and modeling that study the motions of molecules in the dense and dilute phases of biomolecular condensates, with the key finding that molecules in the dense phase of condensates formed by folded domains appear to switch between a confined state with low apparent diffusivity and a mobile state with a high apparent diffusivity that is comparable to that of molecules in the dilute phase. The study provides experimental evidence that is suggestive of phase separation coupled with percolation as the operative mechanism that gives rise to biomolecular condensates.