Disclosed is a recombinant polypeptide for facilitating membrane fusion. The recombinant polypeptide having a sequence with at least 80% sequence identity with the ectodomain of p14 fusion-associated small transmembrane (FAST) protein and having a functional myristoylation motif, a transmembrane domain from a FAST protein and a sequence with at least 80% sequence identity with the endodomain of p15 FAST protein. A targeting ligand can be added to the recombinant polypeptide for selective fusion. The recombinant polypeptide can be included in the membrane of a liposome, or the like, to facilitate the delivery of bioactive compounds, such as siRNA, or the recombinant polypeptide can be mixed with a lipid carrier and added to cultured cells to induce cell-cell fusion and heterokaryon formation.