To demonstrate the versatility of YK-based methodologies, we reconstructed multi-component droplets composed of Nck1 adapter protein and neural Wiskott-Aldrich syndrome protein (N-WASP), which are implicated in actin polymerization within living cells. These tests showed that the lower dynamicity of droplets and the longer dwelling time of N-WASP in droplets enhanced local actin polymerization. Thus, YK systems provide an invaluable tool for the bottom-up construction of multi-component droplets and for investigating protein condensates in mammalian cells.