Initially, we investigated the protein droplet formation by YK-tagging in cells. In accordance with our previous report revealing that tyrosine-rich peptides tend to localize in the nucleus , we appended a nuclear export sequence (NES), from MAPKK2 (36-55) to the N-terminal. By using sfGFP as a model protein, we tested the intracellular droplet formation of NES-YK-tagged sfGFPs by varying number of repeats of YK units (Fig. and Supplementary Fig. ). This led to longer NES-YK13-and NES-YK15-sfGFPs forming fluorescent granules in the cytosol (Fig. and Supplementary Fig. ). The majority of NES-YK11-sfGFP was distributed in cells, while a minority formed puncta. In contrast, the shortest NES-YK9-sfGFP did not show any assemblies.