A sensor for quantification of macromolecular crowding in living cells.

Macromolecular crowding in cells influences processes such as folding, association and diffusion of proteins and polynucleic acids. Direct spatiotemporal readout of crowding would be a powerful approach for unraveling the structure of the cytoplasm and determining the impact of excluded volume on protein function in living cells. Here, we introduce a genetically encodable fluorescence resonance energy transfer (FRET) sensor for quantifying macromolecular crowding and discuss our application of the sensor in bacterial and mammalian cells.