In nature, protein condensates are multi-component systems in which certain subsets of proteins are enriched and cooperatively interact . We leveraged the simple assembly system of YK peptide for the bottom-up construction of multicomponent protein condensates in mammalian cells. To demonstrate this, we fused the NES-YK13 peptide to three fluorescent proteins (sfGFP, mCherry, and miRFP670) and co-expressed them (Fig. ). As a result, they co-assembled into three-component droplets in cells (Fig. ).