Even in the presence of Mg(II), YK13-sfGFP exhibited responsiveness to ATP, forming droplets under crowded conditions (Supplementary Fig. ). The observed droplets in vitro, however, displayed little fluorescence recovery in FRAP experiments, indicating less dynamicity within this timeframe (Supplementary Fig. ). We attributed the discrepancy in dynamicity to the distinct conditions. While NES-YK13-sfGFP within cells existed at high concentrations (> 100 µM) (Supplementary Fig. ), the concentration in test tubes was 5 µM due to the experimental limitations. Additionally, the crowded environment in vitro may differ from the natural cellular environment. Indeed, COS-7 cells expressing NES-YK13-sfGFP were treated with a lysis buffer containing 5% PEG20k, resulting in dynamically arrested protein condensates that showed little recovery in FRAP experiments. Conversely, in the lysis buffer lacking PEG20k, the droplets were dissolved upon dilution (Supplementary Fig. ).