From a chemical perspective, short peptides fabricating artificial coacervate droplets have been developed by taking into account extensive interactions, including van der Waals forces and electrostatic and aromatic interactions . Lysine/arginine-rich cationic peptides associate with anionic biomolecules, forming complex coacervate through electrostatic interactions . Hydrophobic or amphiphilic peptides exhibiting fibrillar assembly can be modified to favor droplet formation . Recently, designed coiled-coil peptides capable of forming network structures have been demonstrated for artificial protein condensates in bacterial cells . However, all of these studies have been limited either to test tubes or within the prokaryotes. Indeed, while K10 or R10 peptides are reported to form droplets in vitro, the peptide-fused superfolder GFPs (sfGFPs) dispersed or localized in the nucleolus in mammalian cells (Supplementary Fig. ). The droplet formation of Tag3-fused sfGFP in bacteria could not be reproduced in mammalian cells. Given the ubiquity of biomolecular condensation in mammalian cells, the development of de novo peptides creating artificial droplets in these cellular contexts is inevitable. The lack of such a platform represents a considerable bottleneck in synthetic biology research on protein condensates.