We noticed that, when these NES-YK13-fused fluorescent proteins were solely expressed, only the sfGFP fusion formed droplets. In the case of fusions with mAG (monomeric Azami-Green 42 ) and mCherry with high monomeric quality , fluorescence was observed uniformly from the cytoplasm, and droplets were scarcely observed (Supplementary Fig. ). Despite the dispersion, NES-YK13-mAG exhibited low fluorescence anisotropy (Supplementary Fig. ), indicating that NES-YK13-mAG formed oligomeric assemblies that were invisible by optical microscopy. Conversely, tetrameric AG fusion, even upon short YK9 fusion, led to aggregates that never recovered fluorescence in the FRAP test (Supplementary Fig. ). Given the impact of YK peptide length on fluidity and the fact that sfGFP dimerizes at high concentrations , we inferred that the reversible polymerization of YK peptides and the weak protein-protein interaction cooperated to form micronscale structures with dynamicity.