YK peptide chain length-dependent oligomer and droplet formation was also observed: YK11-, YK13-, and YK15-sfGFP showed particle sizes of 13.8 ± 3.1, 23.3 ± 0.4, and 28.9 ± 1.9 nm upon the addition of ATP, while YK9-sfGFP remained in a monomeric state even in the presence of ATP (Supplementary Fig. ). Upon the addition of 5% PEG20k, droplets were observed at >5 µM for YK11-sfGFP and at >1 µM for YK13-and YK15-sfGFP, whereas no droplet formation was observed for YK9-sfGFP (Supplementary Fig. ), which is consistent with the YK length dependence observed in living cells.